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# 15 Other Programming Languages

While the presentation of `gettext` focuses mostly on C and implicitly applies to C++ as well, its scope is far broader than that: Many programming languages, scripting languages and other textual data like GUI resources or package descriptions can make use of the gettext approach.

## 15.1 The Language Implementor's View

All programming and scripting languages that have the notion of strings are eligible to supporting `gettext`. Supporting `gettext` means the following:

1. You should add to the language a syntax for translatable strings. In principle, a function call of `gettext` would do, but a shorthand syntax helps keeping the legibility of internationalized programs. For example, in C we use the syntax `_("string")`, and in GNU awk we use the shorthand `_"string"`.
2. You should arrange that evaluation of such a translatable string at runtime calls the `gettext` function, or performs equivalent processing.
3. Similarly, you should make the functions `ngettext`, `dcgettext`, `dcngettext` available from within the language. These functions are less often used, but are nevertheless necessary for particular purposes: `ngettext` for correct plural handling, and `dcgettext` and `dcngettext` for obeying other locale-related environment variables than `LC_MESSAGES`, such as `LC_TIME` or `LC_MONETARY`. For these latter functions, you need to make the `LC_*` constants, available in the C header `<locale.h>`, referenceable from within the language, usually either as enumeration values or as strings.
4. You should allow the programmer to designate a message domain, either by making the `textdomain` function available from within the language, or by introducing a magic variable called `TEXTDOMAIN`. Similarly, you should allow the programmer to designate where to search for message catalogs, by providing access to the `bindtextdomain` function.
5. You should either perform a `setlocale (LC_ALL, "")` call during the startup of your language runtime, or allow the programmer to do so. Remember that gettext will act as a no-op if the `LC_MESSAGES` and `LC_CTYPE` locale categories are not both set.
6. A programmer should have a way to extract translatable strings from a program into a PO file. The GNU `xgettext` program is being extended to support very different programming languages. Please contact the GNU `gettext` maintainers to help them doing this. If the string extractor is best integrated into your language's parser, GNU `xgettext` can function as a front end to your string extractor.
7. The language's library should have a string formatting facility where the arguments of a format string are denoted by a positional number or a name. This is needed because for some languages and some messages with more than one substitutable argument, the translation will need to output the substituted arguments in different order. See section 4.6 Special Comments preceding Keywords.
8. If the language has more than one implementation, and not all of the implementations use `gettext`, but the programs should be portable across implementations, you should provide a no-i18n emulation, that makes the other implementations accept programs written for yours, without actually translating the strings.
9. To help the programmer in the task of marking translatable strings, which is sometimes performed using the Emacs PO mode (see section 4.5 Marking Translatable Strings), you are welcome to contact the GNU `gettext` maintainers, so they can add support for your language to `‘po-mode.el’`.

On the implementation side, three approaches are possible, with different effects on portability and copyright:

- You may integrate the GNU `gettext`'s `‘intl/’` directory in your package, as described in section 13 The Maintainer's View. This allows you to have internationalization on all kinds of platforms. Note that when you then distribute your package, it legally falls under the GNU General Public License, and the GNU project will be glad about your contribution to the Free Software pool.
- You may link against GNU `gettext` functions if they are found in the C library. For example, an autoconf test for `gettext()` and `ngettext()` will detect this situation. For the moment, this test will succeed on GNU systems and not on other platforms. No severe copyright restrictions apply.
- You may emulate or reimplement the GNU `gettext` functionality. This has the advantage of full portability and no copyright restrictions, but also the drawback that you have to reimplement the GNU `gettext` features (such as the `LANGUAGE` environment variable, the locale aliases database, the automatic charset conversion, and plural handling).

## 15.2 The Programmer's View

For the programmer, the general procedure is the same as for the C language. The Emacs PO mode marking supports other languages, and the GNU `xgettext` string extractor recognizes other languages based on the file extension or a command-line option. In some languages, `setlocale` is not needed because it is already performed by the underlying language runtime.

## 15.3 The Translator's View

The translator works exactly as in the C language case. The only difference is that when translating format strings, she has to be aware of the language's particular syntax for positional arguments in format strings.

### 15.3.1 C Format Strings

C format strings are described in POSIX (IEEE P1003.1 2001), section XSH 3 fprintf(), http://www.opengroup.org/onlinepubs/007904975/functions/fprintf.html. See also the fprintf() manual page, http://www.linuxvalley.it/encyclopedia/ldp/manpage/man3/printf.3.php, http://informatik.fh-wuerzburg.de/student/i510/man/printf.html.

Although format strings with positions that reorder arguments, such as

    "Only %2$d bytes free on '%1$s'."

which is semantically equivalent to

    "'%s' has only %d bytes free."

are a POSIX/XSI feature and not specified by ISO C 99, translators can rely on this reordering ability: On the few platforms where `printf()`, `fprintf()` etc. don't support this feature natively, `‘libintl.a’` or `‘libintl.so’` provides replacement functions, and GNU `<libintl.h>` activates these replacement functions automatically.

As a special feature for Farsi (Persian) and maybe Arabic, translators can insert an `‘I’` flag into numeric format directives. For example, the translation of `"%d"` can be `"%Id"`. The effect of this flag, on systems with GNU `libc`, is that in the output, the ASCII digits are replaced with the `‘outdigits’` defined in the `LC_CTYPE` locale category. On other systems, the `gettext` function removes this flag, so that it has no effect.

Note that the programmer should not put this flag into the untranslated string. (Putting the `‘I’` format directive flag into an msgid string would lead to undefined behaviour on platforms without glibc when NLS is disabled.)

### 15.3.2 Objective C Format Strings

Objective C format strings are like C format strings. They support an additional format directive: "%@", which when executed consumes an argument of type `Object *`.

### 15.3.3 Shell Format Strings

Shell format strings, as supported by GNU gettext and the `‘envsubst’` program, are strings with references to shell variables in the form `$variable` or `${variable}`. References of the form `${variable-default}`, `${variable:-default}`, `${variable=default}`, `${variable:=default}`, `${variable+replacement}`, `${variable:+replacement}`, `${variable?ignored}`, `${variable:?ignored}`, that would be valid inside shell scripts, are not supported. The variable names must consist solely of alphanumeric or underscore ASCII characters, not start with a digit and be nonempty; otherwise such a variable reference is ignored.

### 15.3.4 Python Format Strings

There are two kinds of format strings in Python: those acceptable to the Python built-in format operator `%`, labelled as `‘python-format’`, and those acceptable to the `format` method of the `‘str’` object.

Python `%` format strings are described in Python Library reference / 5. Built-in Types / 5.6. Sequence Types / 5.6.2. String Formatting Operations. http://docs.python.org/2/library/stdtypes.html#string-formatting-operations.

Python brace format strings are described in PEP 3101 -- Advanced String Formatting, http://www.python.org/dev/peps/pep-3101/.

### 15.3.5 Lisp Format Strings

Lisp format strings are described in the Common Lisp HyperSpec, chapter 22.3 Formatted Output, http://www.lisp.org/HyperSpec/Body/sec_22-3.html.

### 15.3.6 Emacs Lisp Format Strings

Emacs Lisp format strings are documented in the Emacs Lisp reference, section Formatting Strings, http://www.gnu.org/manual/elisp-manual-21-2.8/html_chapter/elisp_4.html#SEC75. Note that as of version 21, XEmacs supports numbered argument specifications in format strings while FSF Emacs doesn't.

### 15.3.7 librep Format Strings

librep format strings are documented in the librep manual, section Formatted Output, http://librep.sourceforge.net/librep-manual.html#Formatted%20Output, http://www.gwinnup.org/research/docs/librep.html#SEC122.

### 15.3.8 Scheme Format Strings

Scheme format strings are documented in the SLIB manual, section Format Specification.

### 15.3.9 Smalltalk Format Strings

Smalltalk format strings are described in the GNU Smalltalk documentation, class `CharArray`, methods `‘bindWith:’` and `‘bindWithArguments:’`. http://www.gnu.org/software/smalltalk/gst-manual/gst_68.html#SEC238. In summary, a directive starts with `‘%’` and is followed by `‘%’` or a nonzero digit (`‘1’` to `‘9’`).

### 15.3.10 Java Format Strings

Java format strings are described in the JDK documentation for class `java.text.MessageFormat`, http://java.sun.com/j2se/1.4/docs/api/java/text/MessageFormat.html. See also the ICU documentation http://oss.software.ibm.com/icu/apiref/classMessageFormat.html.

### 15.3.11 C# Format Strings

C# format strings are described in the .NET documentation for class `System.String` and in http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpConFormattingOverview.asp.

### 15.3.12 awk Format Strings

awk format strings are described in the gawk documentation, section Printf, http://www.gnu.org/manual/gawk/html_node/Printf.html#Printf.

### 15.3.13 Object Pascal Format Strings

Object Pascal format strings are described in the documentation of the Free Pascal runtime library, section Format, http://www.freepascal.org/docs-html/rtl/sysutils/format.html.

### 15.3.14 YCP Format Strings

YCP sformat strings are described in the libycp documentation file:/usr/share/doc/packages/libycp/YCP-builtins.html. In summary, a directive starts with `‘%’` and is followed by `‘%’` or a nonzero digit (`‘1’` to `‘9’`).

### 15.3.15 Tcl Format Strings

Tcl format strings are described in the `‘format.n’` manual page, http://www.scriptics.com/man/tcl8.3/TclCmd/format.htm.

### 15.3.16 Perl Format Strings

There are two kinds format strings in Perl: those acceptable to the Perl built-in function `printf`, labelled as `‘perl-format’`, and those acceptable to the `libintl-perl` function `__x`, labelled as `‘perl-brace-format’`.

Perl `printf` format strings are described in the `sprintf` section of `‘man perlfunc’`.

Perl brace format strings are described in the `‘Locale::TextDomain(3pm)’` manual page of the CPAN package libintl-perl. In brief, Perl format uses placeholders put between braces (`‘{’` and `‘}’`). The placeholder must have the syntax of simple identifiers.

### 15.3.17 PHP Format Strings

PHP format strings are described in the documentation of the PHP function `sprintf`, in `‘phpdoc/manual/function.sprintf.html’` or http://www.php.net/manual/en/function.sprintf.php.

### 15.3.18 GCC internal Format Strings

These format strings are used inside the GCC sources. In such a format string, a directive starts with `‘%’`, is optionally followed by a size specifier `‘l’`, an optional flag `‘+’`, another optional flag `‘#’`, and is finished by a specifier: `‘%’` denotes a literal percent sign, `‘c’` denotes a character, `‘s’` denotes a string, `‘i’` and `‘d’` denote an integer, `‘o’`, `‘u’`, `‘x’` denote an unsigned integer, `‘.*s’` denotes a string preceded by a width specification, `‘H’` denotes a `‘location_t *’` pointer, `‘D’` denotes a general declaration, `‘F’` denotes a function declaration, `‘T’` denotes a type, `‘A’` denotes a function argument, `‘C’` denotes a tree code, `‘E’` denotes an expression, `‘L’` denotes a programming language, `‘O’` denotes a binary operator, `‘P’` denotes a function parameter, `‘Q’` denotes an assignment operator, `‘V’` denotes a const/volatile qualifier.

### 15.3.19 GFC internal Format Strings

These format strings are used inside the GNU Fortran Compiler sources, that is, the Fortran frontend in the GCC sources. In such a format string, a directive starts with `‘%’` and is finished by a specifier: `‘%’` denotes a literal percent sign, `‘C’` denotes the current source location, `‘L’` denotes a source location, `‘c’` denotes a character, `‘s’` denotes a string, `‘i’` and `‘d’` denote an integer, `‘u’` denotes an unsigned integer. `‘i’`, `‘d’`, and `‘u’` may be preceded by a size specifier `‘l’`.

### 15.3.20 Qt Format Strings

Qt format strings are described in the documentation of the QString class file:/usr/lib/qt-4.3.0/doc/html/qstring.html. In summary, a directive consists of a `‘%’` followed by a digit. The same directive cannot occur more than once in a format string.

### 15.3.21 Qt Format Strings

Qt format strings are described in the documentation of the QObject::tr method file:/usr/lib/qt-4.3.0/doc/html/qobject.html. In summary, the only allowed directive is `‘%n’`.

### 15.3.22 KDE Format Strings

KDE 4 format strings are defined as follows: A directive consists of a `‘%’` followed by a non-zero decimal number. If a `‘%n’` occurs in a format strings, all of `‘%1’`, ..., `‘%(n-1)’` must occur as well, except possibly one of them.

### 15.3.23 KUIT Format Strings

KUIT (KDE User Interface Text) is compatible with KDE 4 format strings, while it also allows programmers to add semantic information to a format string, through XML markup tags. For example, if the first format directive in a string is a filename, programmers could indicate that with a `‘filename’` tag, like `‘<filename>%1</filename>’`.

KUIT format strings are described in http://api.kde.org/frameworks-api/frameworks5-apidocs/ki18n/html/prg_guide.html#kuit_markup.

### 15.3.24 Boost Format Strings

Boost format strings are described in the documentation of the `boost::format` class, at http://www.boost.org/libs/format/doc/format.html. In summary, a directive has either the same syntax as in a C format string, such as `‘%1$+5d’`, or may be surrounded by vertical bars, such as `‘%|1$+5d|’` or `‘%|1$+5|’`, or consists of just an argument number between percent signs, such as `‘%1%’`.

### 15.3.25 Lua Format Strings

Lua format strings are described in the Lua reference manual, section String Manipulation, http://www.lua.org/manual/5.1/manual.html#pdf-string.format.

### 15.3.26 JavaScript Format Strings

Although JavaScript specification itself does not define any format strings, many JavaScript implementations provide printf-like functions. `xgettext` understands a set of common format strings used in popular JavaScript implementations including Gjs, Seed, and Node.JS. In such a format string, a directive starts with `‘%’` and is finished by a specifier: `‘%’` denotes a literal percent sign, `‘c’` denotes a character, `‘s’` denotes a string, `‘b’`, `‘d’`, `‘o’`, `‘x’`, `‘X’` denote an integer, `‘f’` denotes floating-point number, `‘j’` denotes a JSON object.

## 15.4 The Maintainer's View

For the maintainer, the general procedure differs from the C language case in two ways.

- For those languages that don't use GNU gettext, the `‘intl/’` directory is not needed and can be omitted. This means that the maintainer calls the `gettextize` program without the `‘--intl’` option, and that he invokes the `AM_GNU_GETTEXT` autoconf macro via `‘AM_GNU_GETTEXT([external])’`.
- If only a single programming language is used, the `XGETTEXT_OPTIONS` variable in `‘po/Makevars’` (see section 13.4.3 `‘Makevars’` in `‘po/’`) should be adjusted to match the `xgettext` options for that particular programming language. If the package uses more than one programming language with `gettext` support, it becomes necessary to change the POT file construction rule in `‘po/Makefile.in.in’`. It is recommended to make one `xgettext` invocation per programming language, each with the options appropriate for that language, and to combine the resulting files using `msgcat`.

## 15.5 Individual Programming Languages

### 15.5.1 C, C++, Objective C

RPMs
  gcc, gpp, gobjc, glibc, gettext
File extension
  For C: `c`, `h`.
  For C++: `C`, `c++`, `cc`, `cxx`, `cpp`, `hpp`.
  For Objective C: `m`.
String syntax
  `"abc"`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`, `ngettext`, `dngettext`, `dcngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  Programmer must call `setlocale (LC_ALL, "")`
Prerequisite
  `#include <libintl.h>`
  `#include <locale.h>`
  `#define _(string) gettext (string)`
Use or emulate GNU gettext
  Use
Extractor
  `xgettext -k_`
Formatting with positions
  `fprintf "%2$d %1$d"`
  In C++: `autosprintf "%2$d %1$d"` (see section ‘Introduction’ in GNU autosprintf)
Portability
  autoconf (gettext.m4) and #if ENABLE_NLS
po-mode marking
  yes

The following examples are available in the `‘examples’` directory: `hello-c`, `hello-c-gnome`, `hello-c++`, `hello-c++-qt`, `hello-c++-kde`, `hello-c++-gnome`, `hello-c++-wxwidgets`, `hello-objc`, `hello-objc-gnustep`, `hello-objc-gnome`.

### 15.5.2 sh - Shell Script

RPMs
  bash, gettext
File extension
  `sh`
String syntax
  `"abc"`, `'abc'`, `abc`
gettext shorthand
  `"`gettext \"abc\"`"`
gettext/ngettext functions
  `gettext`, `ngettext` programs
  `eval_gettext`, `eval_ngettext` shell functions
textdomain
  environment variable `TEXTDOMAIN`
bindtextdomain
  environment variable `TEXTDOMAINDIR`
setlocale
  automatic
Prerequisite
  `. gettext.sh`
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  ---
Portability
  fully portable
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-sh`.

#### 15.5.2.1 Preparing Shell Scripts for Internationalization

Preparing a shell script for internationalization is conceptually similar to the steps described in section 4 Preparing Program Sources. The concrete steps for shell scripts are as follows.

1. Insert the line

       . gettext.sh

   near the top of the script. `gettext.sh` is a shell function library that provides the functions `eval_gettext` (see section 15.5.2.6 Invoking the `eval_gettext` function) and `eval_ngettext` (see section 15.5.2.7 Invoking the `eval_ngettext` function). You have to ensure that `gettext.sh` can be found in the `PATH`.
2. Set and export the `TEXTDOMAIN` and `TEXTDOMAINDIR` environment variables. Usually `TEXTDOMAIN` is the package or program name, and `TEXTDOMAINDIR` is the absolute pathname corresponding to `$prefix/share/locale`, where `$prefix` is the installation location.

       TEXTDOMAIN=@PACKAGE@
       export TEXTDOMAIN
       TEXTDOMAINDIR=@LOCALEDIR@
       export TEXTDOMAINDIR

3. Prepare the strings for translation, as described in section 4.3 Preparing Translatable Strings.
4. Simplify translatable strings so that they don't contain command substitution (`"`...`"` or `"$(...)"`), variable access with defaulting (like `${variable-default}`), access to positional arguments (like `$0`, `$1`, ...) or highly volatile shell variables (like `$?`). This can always be done through simple local code restructuring. For example,

       echo "Usage: $0 [OPTION] FILE..."

   becomes

       program_name=$0
       echo "Usage: $program_name [OPTION] FILE..."

   Similarly,

       echo "Remaining files: `ls | wc -l`"

   becomes

       filecount="`ls | wc -l`"
       echo "Remaining files: $filecount"

5. For each translatable string, change the output command `‘echo’` or `‘$echo’` to `‘gettext’` (if the string contains no references to shell variables) or to `‘eval_gettext’` (if it refers to shell variables), followed by a no-argument `‘echo’` command (to account for the terminating newline). Similarly, for cases with plural handling, replace a conditional `‘echo’` command with an invocation of `‘ngettext’` or `‘eval_ngettext’`, followed by a no-argument `‘echo’` command. When doing this, you also need to add an extra backslash before the dollar sign in references to shell variables, so that the `‘eval_gettext’` function receives the translatable string before the variable values are substituted into it. For example,

       echo "Remaining files: $filecount"

   becomes

       eval_gettext "Remaining files: \$filecount"; echo

   If the output command is not `‘echo’`, you can make it use `‘echo’` nevertheless, through the use of backquotes. However, note that inside backquotes, backslashes must be doubled to be effective (because the backquoting eats one level of backslashes). For example, assuming that `‘error’` is a shell function that signals an error,

       error "file not found: $filename"

   is first transformed into

       error "`echo \"file not found: \$filename\"`"

   which then becomes

       error "`eval_gettext \"file not found: \\\$filename\"`"

#### 15.5.2.2 Contents of `gettext.sh`

`gettext.sh`, contained in the run-time package of GNU gettext, provides the following:

- $echo The variable `echo` is set to a command that outputs its first argument and a newline, without interpreting backslashes in the argument string.
- eval_gettext See section 15.5.2.6 Invoking the `eval_gettext` function.
- eval_ngettext See section 15.5.2.7 Invoking the `eval_ngettext` function.

#### 15.5.2.3 Invoking the `gettext` program

    gettext [option] [[textdomain] msgid]
    gettext [option] -s [msgid]...

The `gettext` program displays the native language translation of a textual message.

Arguments

`‘-d textdomain’`
`‘--domain=textdomain’`
  Retrieve translated messages from textdomain. Usually a textdomain corresponds to a package, a program, or a module of a program.
`‘-e’`
  Enable expansion of some escape sequences. This option is for compatibility with the `‘echo’` program or shell built-in. The escape sequences `‘\a’`, `‘\b’`, `‘\c’`, `‘\f’`, `‘\n’`, `‘\r’`, `‘\t’`, `‘\v’`, `‘\\’`, and `‘\’` followed by one to three octal digits, are interpreted like the System V `‘echo’` program did.
`‘-E’`
  This option is only for compatibility with the `‘echo’` program or shell built-in. It has no effect.
`‘-h’`
`‘--help’`
  Display this help and exit.
`‘-n’`
  Suppress trailing newline. By default, `gettext` adds a newline to the output.
`‘-V’`
`‘--version’`
  Output version information and exit.
`‘[textdomain] msgid’`
  Retrieve translated message corresponding to msgid from textdomain.

If the textdomain parameter is not given, the domain is determined from the environment variable `TEXTDOMAIN`. If the message catalog is not found in the regular directory, another location can be specified with the environment variable `TEXTDOMAINDIR`.

When used with the `-s` option the program behaves like the `‘echo’` command. But it does not simply copy its arguments to stdout. Instead those messages found in the selected catalog are translated.

Note: `xgettext` supports only the one-argument form of the `gettext` invocation, where no options are present and the textdomain is implicit, from the environment.

#### 15.5.2.4 Invoking the `ngettext` program

    ngettext [option] [textdomain] msgid msgid-plural count

The `ngettext` program displays the native language translation of a textual message whose grammatical form depends on a number.

Arguments

`‘-d textdomain’`
`‘--domain=textdomain’`
  Retrieve translated messages from textdomain. Usually a textdomain corresponds to a package, a program, or a module of a program.
`‘-e’`
  Enable expansion of some escape sequences. This option is for compatibility with the `‘gettext’` program. The escape sequences `‘\a’`, `‘\b’`, `‘\c’`, `‘\f’`, `‘\n’`, `‘\r’`, `‘\t’`, `‘\v’`, `‘\\’`, and `‘\’` followed by one to three octal digits, are interpreted like the System V `‘echo’` program did.
`‘-E’`
  This option is only for compatibility with the `‘gettext’` program. It has no effect.
`‘-h’`
`‘--help’`
  Display this help and exit.
`‘-V’`
`‘--version’`
  Output version information and exit.
`‘textdomain’`
  Retrieve translated message from textdomain.
`‘msgid msgid-plural’`
  Translate msgid (English singular) / msgid-plural (English plural).
`‘count’`
  Choose singular/plural form based on this value.

If the textdomain parameter is not given, the domain is determined from the environment variable `TEXTDOMAIN`. If the message catalog is not found in the regular directory, another location can be specified with the environment variable `TEXTDOMAINDIR`.

Note: `xgettext` supports only the three-arguments form of the `ngettext` invocation, where no options are present and the textdomain is implicit, from the environment.

#### 15.5.2.5 Invoking the `envsubst` program

    envsubst [option] [shell-format]

The `envsubst` program substitutes the values of environment variables.

Operation mode

`‘-v’`
`‘--variables’`
  Output the variables occurring in shell-format.

Informative output

`‘-h’`
`‘--help’`
  Display this help and exit.
`‘-V’`
`‘--version’`
  Output version information and exit.

In normal operation mode, standard input is copied to standard output, with references to environment variables of the form `$VARIABLE` or `${VARIABLE}` being replaced with the corresponding values. If a shell-format is given, only those environment variables that are referenced in shell-format are substituted; otherwise all environment variables references occurring in standard input are substituted.

These substitutions are a subset of the substitutions that a shell performs on unquoted and double-quoted strings. Other kinds of substitutions done by a shell, such as `${variable-default}` or `$(command-list)` or ``command-list``, are not performed by the `envsubst` program, due to security reasons.

When `--variables` is used, standard input is ignored, and the output consists of the environment variables that are referenced in shell-format, one per line.

#### 15.5.2.6 Invoking the `eval_gettext` function

    eval_gettext msgid

This function outputs the native language translation of a textual message, performing dollar-substitution on the result. Note that only shell variables mentioned in msgid will be dollar-substituted in the result.

#### 15.5.2.7 Invoking the `eval_ngettext` function

    eval_ngettext msgid msgid-plural count

This function outputs the native language translation of a textual message whose grammatical form depends on a number, performing dollar-substitution on the result. Note that only shell variables mentioned in msgid or msgid-plural will be dollar-substituted in the result.

### 15.5.3 bash - Bourne-Again Shell Script

GNU `bash` 2.0 or newer has a special shorthand for translating a string and substituting variable values in it: `$"msgid"`. But the use of this construct is discouraged, due to the security holes it opens and due to its portability problems.

The security holes of `$"..."` come from the fact that after looking up the translation of the string, `bash` processes it like it processes any double-quoted string: dollar and backquote processing, like `‘eval’` does.

1. In a locale whose encoding is one of BIG5, BIG5-HKSCS, GBK, GB18030, SHIFT_JIS, JOHAB, some double-byte characters have a second byte whose value is `0x60`. For example, the byte sequence `\xe0\x60` is a single character in these locales. Many versions of `bash` (all versions up to bash-2.05, and newer versions on platforms without `mbsrtowcs()` function) don't know about character boundaries and see a backquote character where there is only a particular Chinese character. Thus it can start executing part of the translation as a command list. This situation can occur even without the translator being aware of it: if the translator provides translations in the UTF-8 encoding, it is the `gettext()` function which will, during its conversion from the translator's encoding to the user's locale's encoding, produce the dangerous `\x60` bytes.
2. A translator could - voluntarily or inadvertently - use backquotes `"`...`"` or dollar-parentheses `"$(...)"` in her translations. The enclosed strings would be executed as command lists by the shell.

The portability problem is that `bash` must be built with internationalization support; this is normally not the case on systems that don't have the `gettext()` function in libc.

### 15.5.4 Python

RPMs
  python
File extension
  `py`
String syntax
  `'abc'`, `u'abc'`, `r'abc'`, `ur'abc'`,
  `"abc"`, `u"abc"`, `r"abc"`, `ur"abc"`,
  `”'abc”'`, `u”'abc”'`, `r”'abc”'`, `ur”'abc”'`,
  `"""abc"""`, `u"""abc"""`, `r"""abc"""`, `ur"""abc"""`
gettext shorthand
  `_('abc')` etc.
gettext/ngettext functions
  `gettext.gettext`, `gettext.dgettext`, `gettext.ngettext`, `gettext.dngettext`, also `ugettext`, `ungettext`
textdomain
  `gettext.textdomain` function, or `gettext.install(domain)` function
bindtextdomain
  `gettext.bindtextdomain` function, or `gettext.install(domain,localedir)` function
setlocale
  not used by the gettext emulation
Prerequisite
  `import gettext`
Use or emulate GNU gettext
  emulate
Extractor
  `xgettext`
Formatting with positions
  `'...%(ident)d...' % { 'ident': value }`
Portability
  fully portable
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-python`.

A note about format strings: Python supports format strings with unnamed arguments, such as `'...%d...'`, and format strings with named arguments, such as `'...%(ident)d...'`. The latter are preferable for internationalized programs, for two reasons:

- When a format string takes more than one argument, the translator can provide a translation that uses the arguments in a different order, if the format string uses named arguments. For example, the translator can reformulate

      "'%(volume)s' has only %(freespace)d bytes free."

  to

      "Only %(freespace)d bytes free on '%(volume)s'."

  Additionally, the identifiers also provide some context to the translator.
- In the context of plural forms, the format string used for the singular form does not use the numeric argument in many languages. Even in English, one prefers to write `"one hour"` instead of `"1 hour"`. Omitting individual arguments from format strings like this is only possible with the named argument syntax. (With unnamed arguments, Python -- unlike C -- verifies that the format string uses all supplied arguments.)

### 15.5.5 GNU clisp - Common Lisp

RPMs
  clisp 2.28 or newer
File extension
  `lisp`
String syntax
  `"abc"`
gettext shorthand
  `(_ "abc")`, `(ENGLISH "abc")`
gettext/ngettext functions
  `i18n:gettext`, `i18n:ngettext`
textdomain
  `i18n:textdomain`
bindtextdomain
  `i18n:textdomaindir`
setlocale
  automatic
Prerequisite
  ---
Use or emulate GNU gettext
  use
Extractor
  `xgettext -k_ -kENGLISH`
Formatting with positions
  `format "~1@*~D ~0@*~D"`
Portability
  On platforms without gettext, no translation.
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-clisp`.

### 15.5.6 GNU clisp C sources

RPMs
  clisp
File extension
  `d`
String syntax
  `"abc"`
gettext shorthand
  `ENGLISH ? "abc" : ""`
  `GETTEXT("abc")`
  `GETTEXTL("abc")`
gettext/ngettext functions
  `clgettext`, `clgettextl`
textdomain
  ---
bindtextdomain
  ---
setlocale
  automatic
Prerequisite
  `#include "lispbibl.c"`
Use or emulate GNU gettext
  use
Extractor
  `clisp-xgettext`
Formatting with positions
  `fprintf "%2$d %1$d"`
Portability
  On platforms without gettext, no translation.
po-mode marking
  ---

### 15.5.7 Emacs Lisp

RPMs
  emacs, xemacs
File extension
  `el`
String syntax
  `"abc"`
gettext shorthand
  `(_"abc")`
gettext/ngettext functions
  `gettext`, `dgettext` (xemacs only)
textdomain
  `domain` special form (xemacs only)
bindtextdomain
  `bind-text-domain` function (xemacs only)
setlocale
  automatic
Prerequisite
  ---
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  `format "%2$d %1$d"`
Portability
  Only XEmacs. Without `I18N3` defined at build time, no translation.
po-mode marking
  ---

### 15.5.8 librep

RPMs
  librep 0.15.3 or newer
File extension
  `jl`
String syntax
  `"abc"`
gettext shorthand
  `(_"abc")`
gettext/ngettext functions
  `gettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  ---
Prerequisite
  `(require 'rep.i18n.gettext)`
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  `format "%2$d %1$d"`
Portability
  On platforms without gettext, no translation.
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-librep`.

### 15.5.9 GNU guile - Scheme

RPMs
  guile
File extension
  `scm`
String syntax
  `"abc"`
gettext shorthand
  `(_ "abc")`, `_"abc"` (GIMP script-fu extension)
gettext/ngettext functions
  `gettext`, `ngettext`
textdomain
  `textdomain`
bindtextdomain
  `bindtextdomain`
setlocale
  `(catch #t (lambda () (setlocale LC_ALL "")) (lambda args #f))`
Prerequisite
  `(use-modules (ice-9 format))`
Use or emulate GNU gettext
  use
Extractor
  `xgettext -k_`
Formatting with positions
  ---
Portability
  On platforms without gettext, no translation.
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-guile`.

### 15.5.10 GNU Smalltalk

RPMs
  smalltalk
File extension
  `st`
String syntax
  `'abc'`
gettext shorthand
  `NLS ? 'abc'`
gettext/ngettext functions
  `LcMessagesDomain>>#at:`, `LcMessagesDomain>>#at:plural:with:`
textdomain
  `LcMessages>>#domain:localeDirectory:` (returns a `LcMessagesDomain` object).
  Example: `I18N Locale default messages domain: 'gettext' localeDirectory: /usr/local/share/locale'`
bindtextdomain
  `LcMessages>>#domain:localeDirectory:`, see above.
setlocale
  Automatic if you use `I18N Locale default`.
Prerequisite
  `PackageLoader fileInPackage: 'I18N'!`
Use or emulate GNU gettext
  emulate
Extractor
  `xgettext`
Formatting with positions
  `'%1 %2' bindWith: 'Hello' with: 'world'`
Portability
  fully portable
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-smalltalk`.

### 15.5.11 Java

RPMs
  java, java2
File extension
  `java`
String syntax
  "abc"
gettext shorthand
  _("abc")
gettext/ngettext functions
  `GettextResource.gettext`, `GettextResource.ngettext`, `GettextResource.pgettext`, `GettextResource.npgettext`
textdomain
  ---, use `ResourceBundle.getResource` instead
bindtextdomain
  ---, use CLASSPATH instead
setlocale
  automatic
Prerequisite
  ---
Use or emulate GNU gettext
  ---, uses a Java specific message catalog format
Extractor
  `xgettext -k_`
Formatting with positions
  `MessageFormat.format "{1,number} {0,number}"`
Portability
  fully portable
po-mode marking
  ---

Before marking strings as internationalizable, uses of the string concatenation operator need to be converted to `MessageFormat` applications. For example, `"file "+filename+" not found"` becomes `MessageFormat.format("file {0} not found", new Object[] { filename })`. Only after this is done, can the strings be marked and extracted.

GNU gettext uses the native Java internationalization mechanism, namely `ResourceBundle`s. There are two formats of `ResourceBundle`s: `.properties` files and `.class` files. The `.properties` format is a text file which the translators can directly edit, like PO files, but which doesn't support plural forms. Whereas the `.class` format is compiled from `.java` source code and can support plural forms (provided it is accessed through an appropriate API, see below).

To convert a PO file to a `.properties` file, the `msgcat` program can be used with the option `--properties-output`. To convert a `.properties` file back to a PO file, the `msgcat` program can be used with the option `--properties-input`. All the tools that manipulate PO files can work with `.properties` files as well, if given the `--properties-input` and/or `--properties-output` option.

To convert a PO file to a ResourceBundle class, the `msgfmt` program can be used with the option `--java` or `--java2`. To convert a ResourceBundle back to a PO file, the `msgunfmt` program can be used with the option `--java`.

Two different programmatic APIs can be used to access ResourceBundles. Note that both APIs work with all kinds of ResourceBundles, whether GNU gettext generated classes, or other `.class` or `.properties` files.

1. The `java.util.ResourceBundle` API. In particular, its `getString` function returns a string translation. Note that a missing translation yields a `MissingResourceException`. This has the advantage of being the standard API. And it does not require any additional libraries, only the `msgcat` generated `.properties` files or the `msgfmt` generated `.class` files. But it cannot do plural handling, even if the resource was generated by `msgfmt` from a PO file with plural handling.
2. The `gnu.gettext.GettextResource` API. Reference documentation in Javadoc 1.1 style format is in the javadoc2 directory. Its `gettext` function returns a string translation. Note that when a translation is missing, the msgid argument is returned unchanged. This has the advantage of having the `ngettext` function for plural handling and the `pgettext` and `npgettext` for strings constraint to a particular context. To use this API, one needs the `libintl.jar` file which is part of the GNU gettext package and distributed under the LGPL.

Four examples, using the second API, are available in the `‘examples’` directory: `hello-java`, `hello-java-awt`, `hello-java-swing`, `hello-java-qtjambi`.

Now, to make use of the API and define a shorthand for `‘getString’`, there are three idioms that you can choose from:

- (This one assumes Java 1.5 or newer.) In a unique class of your project, say `‘Util’`, define a static variable holding the `ResourceBundle` instance and the shorthand:

      private static ResourceBundle myResources =
        ResourceBundle.getBundle("domain-name");
      public static String _(String s) {
        return myResources.getString(s);
      }

  All classes containing internationalized strings then contain

      import static Util._;

  and the shorthand is used like this:

      System.out.println(_("Operation completed."));

- In a unique class of your project, say `‘Util’`, define a static variable holding the `ResourceBundle` instance:

      public static ResourceBundle myResources =
        ResourceBundle.getBundle("domain-name");

  All classes containing internationalized strings then contain

      private static ResourceBundle res = Util.myResources;
      private static String _(String s) { return res.getString(s); }

  and the shorthand is used like this:

      System.out.println(_("Operation completed."));

- You add a class with a very short name, say `‘S’`, containing just the definition of the resource bundle and of the shorthand:

      public class S {
        public static ResourceBundle myResources =
          ResourceBundle.getBundle("domain-name");
        public static String _(String s) {
          return myResources.getString(s);
        }
      }

  and the shorthand is used like this:

      System.out.println(S._("Operation completed."));

Which of the three idioms you choose, will depend on whether your project requires portability to Java versions prior to Java 1.5 and, if so, whether copying two lines of codes into every class is more acceptable in your project than a class with a single-letter name.

### 15.5.12 C#

RPMs
  pnet, pnetlib 0.6.2 or newer, or mono 0.29 or newer
File extension
  `cs`
String syntax
  `"abc"`, `@"abc"`
gettext shorthand
  _("abc")
gettext/ngettext functions
  `GettextResourceManager.GetString`, `GettextResourceManager.GetPluralString` `GettextResourceManager.GetParticularString` `GettextResourceManager.GetParticularPluralString`
textdomain
  `new GettextResourceManager(domain)`
bindtextdomain
  ---, compiled message catalogs are located in subdirectories of the directory containing the executable
setlocale
  automatic
Prerequisite
  ---
Use or emulate GNU gettext
  ---, uses a C# specific message catalog format
Extractor
  `xgettext -k_`
Formatting with positions
  `String.Format "{1} {0}"`
Portability
  fully portable
po-mode marking
  ---

Before marking strings as internationalizable, uses of the string concatenation operator need to be converted to `String.Format` invocations. For example, `"file "+filename+" not found"` becomes `String.Format("file {0} not found", filename)`. Only after this is done, can the strings be marked and extracted.

GNU gettext uses the native C#/.NET internationalization mechanism, namely the classes `ResourceManager` and `ResourceSet`. Applications use the `ResourceManager` methods to retrieve the native language translation of strings. An instance of `ResourceSet` is the in-memory representation of a message catalog file. The `ResourceManager` loads and accesses `ResourceSet` instances as needed to look up the translations.

There are two formats of `ResourceSet`s that can be directly loaded by the C# runtime: `.resources` files and `.dll` files.

- The `.resources` format is a binary file usually generated through the `resgen` or `monoresgen` utility, but which doesn't support plural forms. `.resources` files can also be embedded in .NET `.exe` files. This only affects whether a file system access is performed to load the message catalog; it doesn't affect the contents of the message catalog.
- On the other hand, the `.dll` format is a binary file that is compiled from `.cs` source code and can support plural forms (provided it is accessed through the GNU gettext API, see below).

Note that these .NET `.dll` and `.exe` files are not tied to a particular platform; their file format and GNU gettext for C# can be used on any platform.

To convert a PO file to a `.resources` file, the `msgfmt` program can be used with the option `‘--csharp-resources’`. To convert a `.resources` file back to a PO file, the `msgunfmt` program can be used with the option `‘--csharp-resources’`. You can also, in some cases, use the `resgen` program (from the `pnet` package) or the `monoresgen` program (from the `mono`/`mcs` package). These programs can also convert a `.resources` file back to a PO file. But beware: as of this writing (January 2004), the `monoresgen` converter is quite buggy and the `resgen` converter ignores the encoding of the PO files.

To convert a PO file to a `.dll` file, the `msgfmt` program can be used with the option `--csharp`. The result will be a `.dll` file containing a subclass of `GettextResourceSet`, which itself is a subclass of `ResourceSet`. To convert a `.dll` file containing a `GettextResourceSet` subclass back to a PO file, the `msgunfmt` program can be used with the option `--csharp`.

The advantages of the `.dll` format over the `.resources` format are:

1. Freedom to localize: Users can add their own translations to an application after it has been built and distributed. Whereas when the programmer uses a `ResourceManager` constructor provided by the system, the set of `.resources` files for an application must be specified when the application is built and cannot be extended afterwards.
2. Plural handling: A message catalog in `.dll` format supports the plural handling function `GetPluralString`. Whereas `.resources` files can only contain data and only support lookups that depend on a single string.
3. Context handling: A message catalog in `.dll` format supports the query-with-context functions `GetParticularString` and `GetParticularPluralString`. Whereas `.resources` files can only contain data and only support lookups that depend on a single string.
4. The `GettextResourceManager` that loads the message catalogs in `.dll` format also provides for inheritance on a per-message basis. For example, in Austrian (`de_AT`) locale, translations from the German (`de`) message catalog will be used for messages not found in the Austrian message catalog. This has the consequence that the Austrian translators need only translate those few messages for which the translation into Austrian differs from the German one. Whereas when working with `.resources` files, each message catalog must provide the translations of all messages by itself.
5. The `GettextResourceManager` that loads the message catalogs in `.dll` format also provides for a fallback: The English msgid is returned when no translation can be found. Whereas when working with `.resources` files, a language-neutral `.resources` file must explicitly be provided as a fallback.

On the side of the programmatic APIs, the programmer can use either the standard `ResourceManager` API and the GNU `GettextResourceManager` API. The latter is an extension of the former, because `GettextResourceManager` is a subclass of `ResourceManager`.

1. The `System.Resources.ResourceManager` API. This API works with resources in `.resources` format. The creation of the `ResourceManager` is done through

         new ResourceManager(domainname, Assembly.GetExecutingAssembly())

   The `GetString` function returns a string's translation. Note that this function returns null when a translation is missing (i.e. not even found in the fallback resource file).
2. The `GNU.Gettext.GettextResourceManager` API. This API works with resources in `.dll` format. Reference documentation is in the csharpdoc directory. The creation of the `ResourceManager` is done through

         new GettextResourceManager(domainname)

   The `GetString` function returns a string's translation. Note that when a translation is missing, the msgid argument is returned unchanged. The `GetPluralString` function returns a string translation with plural handling, like the `ngettext` function in C. The `GetParticularString` function returns a string's translation, specific to a particular context, like the `pgettext` function in C. Note that when a translation is missing, the msgid argument is returned unchanged. The `GetParticularPluralString` function returns a string translation, specific to a particular context, with plural handling, like the `npgettext` function in C. To use this API, one needs the `GNU.Gettext.dll` file which is part of the GNU gettext package and distributed under the LGPL.

You can also mix both approaches: use the `GNU.Gettext.GettextResourceManager` constructor, but otherwise use only the `ResourceManager` type and only the `GetString` method. This is appropriate when you want to profit from the tools for PO files, but don't want to change an existing source code that uses `ResourceManager` and don't (yet) need the `GetPluralString` method.

Two examples, using the second API, are available in the `‘examples’` directory: `hello-csharp`, `hello-csharp-forms`.

Now, to make use of the API and define a shorthand for `‘GetString’`, there are two idioms that you can choose from:

- In a unique class of your project, say `‘Util’`, define a static variable holding the `ResourceManager` instance:

      public static GettextResourceManager MyResourceManager =
        new GettextResourceManager("domain-name");

  All classes containing internationalized strings then contain

      private static GettextResourceManager Res = Util.MyResourceManager;
      private static String _(String s) { return Res.GetString(s); }

  and the shorthand is used like this:

      Console.WriteLine(_("Operation completed."));

- You add a class with a very short name, say `‘S’`, containing just the definition of the resource manager and of the shorthand:

      public class S {
        public static GettextResourceManager MyResourceManager =
          new GettextResourceManager("domain-name");
        public static String _(String s) {
           return MyResourceManager.GetString(s);
        }
      }

  and the shorthand is used like this:

      Console.WriteLine(S._("Operation completed."));

Which of the two idioms you choose, will depend on whether copying two lines of codes into every class is more acceptable in your project than a class with a single-letter name.

### 15.5.13 GNU awk

RPMs
  gawk 3.1 or newer
File extension
  `awk`, `gawk`, `twjr`. The file extension `twjr` is used by TexiWeb Jr (https://github.com/arnoldrobbins/texiwebjr).
String syntax
  `"abc"`
gettext shorthand
  `_"abc"`
gettext/ngettext functions
  `dcgettext`, missing `dcngettext` in gawk-3.1.0
textdomain
  `TEXTDOMAIN` variable
bindtextdomain
  `bindtextdomain` function
setlocale
  automatic, but missing `setlocale (LC_MESSAGES, "")` in gawk-3.1.0
Prerequisite
  ---
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  `printf "%2$d %1$d"` (GNU awk only)
Portability
  On platforms without gettext, no translation. On non-GNU awks, you must define `dcgettext`, `dcngettext` and `bindtextdomain` yourself.
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-gawk`.

### 15.5.14 Pascal - Free Pascal Compiler

RPMs
  fpk
File extension
  `pp`, `pas`
String syntax
  `'abc'`
gettext shorthand
  automatic
gettext/ngettext functions
  ---, use `ResourceString` data type instead
textdomain
  ---, use `TranslateResourceStrings` function instead
bindtextdomain
  ---, use `TranslateResourceStrings` function instead
setlocale
  automatic, but uses only LANG, not LC_MESSAGES or LC_ALL
Prerequisite
  `{$mode delphi}` or `{$mode objfpc}`
  `uses gettext;`
Use or emulate GNU gettext
  emulate partially
Extractor
  `ppc386` followed by `xgettext` or `rstconv`
Formatting with positions
  `uses sysutils;`
  `format "%1:d %0:d"`
Portability
  ?
po-mode marking
  ---

The Pascal compiler has special support for the `ResourceString` data type. It generates a `.rst` file. This is then converted to a `.pot` file by use of `xgettext` or `rstconv`. At runtime, a `.mo` file corresponding to translations of this `.pot` file can be loaded using the `TranslateResourceStrings` function in the `gettext` unit.

An example is available in the `‘examples’` directory: `hello-pascal`.

### 15.5.15 wxWidgets library

RPMs
  wxGTK, gettext
File extension
  `cpp`
String syntax
  `"abc"`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `wxLocale::GetString`, `wxGetTranslation`
textdomain
  `wxLocale::AddCatalog`
bindtextdomain
  `wxLocale::AddCatalogLookupPathPrefix`
setlocale
  `wxLocale::Init`, `wxSetLocale`
Prerequisite
  `#include <wx/intl.h>`
Use or emulate GNU gettext
  emulate, see `include/wx/intl.h` and `src/common/intl.cpp`
Extractor
  `xgettext`
Formatting with positions
  wxString::Format supports positions if and only if the system has `wprintf()`, `vswprintf()` functions and they support positions according to POSIX.
Portability
  fully portable
po-mode marking
  yes

### 15.5.16 YCP - YaST2 scripting language

RPMs
  libycp, libycp-devel, yast2-core, yast2-core-devel
File extension
  `ycp`
String syntax
  `"abc"`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `_()` with 1 or 3 arguments
textdomain
  `textdomain` statement
bindtextdomain
  ---
setlocale
  ---
Prerequisite
  ---
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  `sformat "%2 %1"`
Portability
  fully portable
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-ycp`.

### 15.5.17 Tcl - Tk's scripting language

RPMs
  tcl
File extension
  `tcl`
String syntax
  `"abc"`
gettext shorthand
  `[_ "abc"]`
gettext/ngettext functions
  `::msgcat::mc`
textdomain
  ---
bindtextdomain
  ---, use `::msgcat::mcload` instead
setlocale
  automatic, uses LANG, but ignores LC_MESSAGES and LC_ALL
Prerequisite
  `package require msgcat`
  `proc _ {s} {return [::msgcat::mc $s]}`
Use or emulate GNU gettext
  ---, uses a Tcl specific message catalog format
Extractor
  `xgettext -k_`
Formatting with positions
  `format "%2\$d %1\$d"`
Portability
  fully portable
po-mode marking
  ---

Two examples are available in the `‘examples’` directory: `hello-tcl`, `hello-tcl-tk`.

Before marking strings as internationalizable, substitutions of variables into the string need to be converted to `format` applications. For example, `"file $filename not found"` becomes `[format "file %s not found" $filename]`. Only after this is done, can the strings be marked and extracted. After marking, this example becomes `[format [_ "file %s not found"] $filename]` or `[msgcat::mc "file %s not found" $filename]`. Note that the `msgcat::mc` function implicitly calls `format` when more than one argument is given.

### 15.5.18 Perl

RPMs
  perl
File extension
  `pl`, `PL`, `pm`, `perl`, `cgi`
String syntax
  - `"abc"`
  - `'abc'`
  - `qq (abc)`
  - `q (abc)`
  - `qr /abc/`
  - `qx (/bin/date)`
  - `/pattern match/`
  - `?pattern match?`
  - `s/substitution/operators/`
  - `$tied_hash{"message"}`
  - `$tied_hash_reference->{"message"}`
  - etc., issue the command `‘man perlsyn’` for details
gettext shorthand
  `__` (double underscore)
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`, `ngettext`, `dngettext`, `dcngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
bind_textdomain_codeset
  `bind_textdomain_codeset` function
setlocale
  Use `setlocale (LC_ALL, "");`
Prerequisite
  `use POSIX;`
  `use Locale::TextDomain;` (included in the package libintl-perl which is available on the Comprehensive Perl Archive Network CPAN, http://www.cpan.org/).
Use or emulate GNU gettext
  platform dependent: gettext_pp emulates, gettext_xs uses GNU gettext
Extractor
  `xgettext -k__ -k\$__ -k%__ -k__x -k__n:1,2 -k__nx:1,2 -k__xn:1,2 -kN__ -k`
Formatting with positions
  Both kinds of format strings support formatting with positions.
  `printf "%2\$d %1\$d", ...` (requires Perl 5.8.0 or newer)
  `__expand("[new] replaces [old]", old => $oldvalue, new => $newvalue)`
Portability
  The `libintl-perl` package is platform independent but is not part of the Perl core. The programmer is responsible for providing a dummy implementation of the required functions if the package is not installed on the target system.
po-mode marking
  ---
Documentation
  Included in `libintl-perl`, available on CPAN (http://www.cpan.org/).

An example is available in the `‘examples’` directory: `hello-perl`.

The `xgettext` parser backend for Perl differs significantly from the parser backends for other programming languages, just as Perl itself differs significantly from other programming languages. The Perl parser backend offers many more string marking facilities than the other backends but it also has some Perl specific limitations, the worst probably being its imperfectness.

#### 15.5.18.1 General Problems Parsing Perl Code

It is often heard that only Perl can parse Perl. This is not true. Perl cannot be parsed at all, it can only be executed. Perl has various built-in ambiguities that can only be resolved at runtime.

The following example may illustrate one common problem:

    print gettext "Hello World!";

Although this example looks like a bullet-proof case of a function invocation, it is not:

    open gettext, ">testfile" or die;
    print gettext "Hello world!"

In this context, the string `gettext` looks more like a file handle. But not necessarily:

    use Locale::Messages qw (:libintl_h);
    open gettext ">testfile" or die;
    print gettext "Hello world!";

Now, the file is probably syntactically incorrect, provided that the module `Locale::Messages` found first in the Perl include path exports a function `gettext`. But what if the module `Locale::Messages` really looks like this?

    use vars qw (*gettext);

    1;

In this case, the string `gettext` will be interpreted as a file handle again, and the above example will create a file `‘testfile’` and write the string “Hello world!” into it. Even advanced control flow analysis will not really help:

    if (0.5 < rand) {
       eval "use Sane";
    } else {
       eval "use InSane";
    }
    print gettext "Hello world!";

If the module `Sane` exports a function `gettext` that does what we expect, and the module `InSane` opens a file for writing and associates the handle `gettext` with this output stream, we are clueless again about what will happen at runtime. It is completely unpredictable. The truth is that Perl has so many ways to fill its symbol table at runtime that it is impossible to interpret a particular piece of code without executing it.

Of course, `xgettext` will not execute your Perl sources while scanning for translatable strings, but rather use heuristics in order to guess what you meant.

Another problem is the ambiguity of the slash and the question mark. Their interpretation depends on the context:

    # A pattern match.
    print "OK\n" if /foobar/;

    # A division.
    print 1 / 2;

    # Another pattern match.
    print "OK\n" if ?foobar?;

    # Conditional.
    print $x ? "foo" : "bar";

The slash may either act as the division operator or introduce a pattern match, whereas the question mark may act as the ternary conditional operator or as a pattern match, too. Other programming languages like `awk` present similar problems, but the consequences of a misinterpretation are particularly nasty with Perl sources. In `awk` for instance, a statement can never exceed one line and the parser can recover from a parsing error at the next newline and interpret the rest of the input stream correctly. Perl is different, as a pattern match is terminated by the next appearance of the delimiter (the slash or the question mark) in the input stream, regardless of the semantic context. If a slash is really a division sign but mis-interpreted as a pattern match, the rest of the input file is most probably parsed incorrectly.

There are certain cases, where the ambiguity cannot be resolved at all:

    $x = wantarray ? 1 : 0;

The Perl built-in function `wantarray` does not accept any arguments. The Perl parser therefore knows that the question mark does not start a regular expression but is the ternary conditional operator.

    sub wantarrays {}
    $x = wantarrays ? 1 : 0;

Now the situation is different. The function `wantarrays` takes a variable number of arguments (like any non-prototyped Perl function). The question mark is now the delimiter of a pattern match, and hence the piece of code does not compile.

    sub wantarrays() {}
    $x = wantarrays ? 1 : 0;

Now the function is prototyped, Perl knows that it does not accept any arguments, and the question mark is therefore interpreted as the ternaray operator again. But that unfortunately outsmarts `xgettext`.

The Perl parser in `xgettext` cannot know whether a function has a prototype and what that prototype would look like. It therefore makes an educated guess. If a function is known to be a Perl built-in and this function does not accept any arguments, a following question mark or slash is treated as an operator, otherwise as the delimiter of a following regular expression. The Perl built-ins that do not accept arguments are `wantarray`, `fork`, `time`, `times`, `getlogin`, `getppid`, `getpwent`, `getgrent`, `gethostent`, `getnetent`, `getprotoent`, `getservent`, `setpwent`, `setgrent`, `endpwent`, `endgrent`, `endhostent`, `endnetent`, `endprotoent`, and `endservent`.

If you find that `xgettext` fails to extract strings from portions of your sources, you should therefore look out for slashes and/or question marks preceding these sections. You may have come across a bug in `xgettext`'s Perl parser (and of course you should report that bug). In the meantime you should consider to reformulate your code in a manner less challenging to `xgettext`.

In particular, if the parser is too dumb to see that a function does not accept arguments, use parentheses:

    $x = somefunc() ? 1 : 0;
    $y = (somefunc) ? 1 : 0;

In fact the Perl parser itself has similar problems and warns you about such constructs.

#### 15.5.18.2 Which keywords will xgettext look for?

Unless you instruct `xgettext` otherwise by invoking it with one of the options `--keyword` or `-k`, it will recognize the following keywords in your Perl sources:

- `gettext`
- `dgettext`
- `dcgettext`
- `ngettext:1,2` The first (singular) and the second (plural) argument will be extracted.
- `dngettext:1,2` The first (singular) and the second (plural) argument will be extracted.
- `dcngettext:1,2` The first (singular) and the second (plural) argument will be extracted.
- `gettext_noop`
- `%gettext` The keys of lookups into the hash `%gettext` will be extracted.
- `$gettext` The keys of lookups into the hash reference `$gettext` will be extracted.

#### 15.5.18.3 How to Extract Hash Keys

Translating messages at runtime is normally performed by looking up the original string in the translation database and returning the translated version. The “natural” Perl implementation is a hash lookup, and, of course, `xgettext` supports such practice.

    print __"Hello world!";
    print $__{"Hello world!"};
    print $__->{"Hello world!"};
    print $$__{"Hello world!"};

The above four lines all do the same thing. The Perl module `Locale::TextDomain` exports by default a hash `%__` that is tied to the function `__()`. It also exports a reference `$__` to `%__`.

If an argument to the `xgettext` option `--keyword`, resp. `-k` starts with a percent sign, the rest of the keyword is interpreted as the name of a hash. If it starts with a dollar sign, the rest of the keyword is interpreted as a reference to a hash.

Note that you can omit the quotation marks (single or double) around the hash key (almost) whenever Perl itself allows it:

    print $gettext{Error};

The exact rule is: You can omit the surrounding quotes, when the hash key is a valid C (!) identifier, i.e. when it starts with an underscore or an ASCII letter and is followed by an arbitrary number of underscores, ASCII letters or digits. Other Unicode characters are not allowed, regardless of the `use utf8` pragma.

#### 15.5.18.4 What are Strings And Quote-like Expressions?

Perl offers a plethora of different string constructs. Those that can be used either as arguments to functions or inside braces for hash lookups are generally supported by `xgettext`.

- double-quoted strings

      print gettext "Hello World!";

- single-quoted strings

      print gettext 'Hello World!';

- the operator qq

      print gettext qq |Hello World!|;
      print gettext qq <E-mail: <guido\@imperia.net>>;

  The operator `qq` is fully supported. You can use arbitrary delimiters, including the four bracketing delimiters (round, angle, square, curly) that nest.
- the operator q

      print gettext q |Hello World!|;
      print gettext q <E-mail: <guido@imperia.net>>;

  The operator `q` is fully supported. You can use arbitrary delimiters, including the four bracketing delimiters (round, angle, square, curly) that nest.
- the operator qx

      print gettext qx ;LANGUAGE=C /bin/date;
      print gettext qx [/usr/bin/ls | grep '^[A-Z]*'];

  The operator `qx` is fully supported. You can use arbitrary delimiters, including the four bracketing delimiters (round, angle, square, curly) that nest. The example is actually a useless use of `gettext`. It will invoke the `gettext` function on the output of the command specified with the `qx` operator. The feature was included in order to make the interface consistent (the parser will extract all strings and quote-like expressions).
- here documents

      print gettext <<'EOF';
      program not found in $PATH
      EOF

      print ngettext <<EOF, <<"EOF";
      one file deleted
      EOF
      several files deleted
      EOF

  Here-documents are recognized. If the delimiter is enclosed in single quotes, the string is not interpolated. If it is enclosed in double quotes or has no quotes at all, the string is interpolated. Delimiters that start with a digit are not supported!

#### 15.5.18.5 Invalid Uses Of String Interpolation

Perl is capable of interpolating variables into strings. This offers some nice features in localized programs but can also lead to problems.

A common error is a construct like the following:

    print gettext "This is the program $0!\n";

Perl will interpolate at runtime the value of the variable `$0` into the argument of the `gettext()` function. Hence, this argument is not a string constant but a variable argument (`$0` is a global variable that holds the name of the Perl script being executed). The interpolation is performed by Perl before the string argument is passed to `gettext()` and will therefore depend on the name of the script which can only be determined at runtime. Consequently, it is almost impossible that a translation can be looked up at runtime (except if, by accident, the interpolated string is found in the message catalog).

The `xgettext` program will therefore terminate parsing with a fatal error if it encounters a variable inside of an extracted string. In general, this will happen for all kinds of string interpolations that cannot be safely performed at compile time. If you absolutely know what you are doing, you can always circumvent this behavior:

    my $know_what_i_am_doing = "This is program $0!\n";
    print gettext $know_what_i_am_doing;

Since the parser only recognizes strings and quote-like expressions, but not variables or other terms, the above construct will be accepted. You will have to find another way, however, to let your original string make it into your message catalog.

If invoked with the option `--extract-all`, resp. `-a`, variable interpolation will be accepted. Rationale: You will generally use this option in order to prepare your sources for internationalization.

Please see the manual page `‘man perlop’` for details of strings and quote-like expressions that are subject to interpolation and those that are not. Safe interpolations (that will not lead to a fatal error) are:

- the escape sequences `\t` (tab, HT, TAB), `\n` (newline, NL), `\r` (return, CR), `\f` (form feed, FF), `\b` (backspace, BS), `\a` (alarm, bell, BEL), and `\e` (escape, ESC).
- octal chars, like `\033`
  Note that octal escapes in the range of 400-777 are translated into a UTF-8 representation, regardless of the presence of the `use utf8` pragma.
- hex chars, like `\x1b`
- wide hex chars, like `\x{263a}`
  Note that this escape is translated into a UTF-8 representation, regardless of the presence of the `use utf8` pragma.
- control chars, like `\c[` (CTRL-[)
- named Unicode chars, like `\N{LATIN CAPITAL LETTER C WITH CEDILLA}`
  Note that this escape is translated into a UTF-8 representation, regardless of the presence of the `use utf8` pragma.

The following escapes are considered partially safe:

- `\l` lowercase next char
- `\u` uppercase next char
- `\L` lowercase till \E
- `\U` uppercase till \E
- `\E` end case modification
- `\Q` quote non-word characters till \E

These escapes are only considered safe if the string consists of ASCII characters only. Translation of characters outside the range defined by ASCII is locale-dependent and can actually only be performed at runtime; `xgettext` doesn't do these locale-dependent translations at extraction time.

Except for the modifier `\Q`, these translations, albeit valid, are generally useless and only obfuscate your sources. If a translation can be safely performed at compile time you can just as well write what you mean.

#### 15.5.18.6 Valid Uses Of String Interpolation

Perl is often used to generate sources for other programming languages or arbitrary file formats. Web applications that output HTML code make a prominent example for such usage.

You will often come across situations where you want to intersperse code written in the target (programming) language with translatable messages, like in the following HTML example:

    print gettext <<EOF;
    <h1>My Homepage</h1>
    <script language="JavaScript"><!--
    for (i = 0; i < 100; ++i) {
        alert ("Thank you so much for visiting my homepage!");
    }
    //--></script>
    EOF

The parser will extract the entire here document, and it will appear entirely in the resulting PO file, including the JavaScript snippet embedded in the HTML code. If you exaggerate with constructs like the above, you will run the risk that the translators of your package will look out for a less challenging project. You should consider an alternative expression here:

    print <<EOF;
    <h1>$gettext{"My Homepage"}</h1>
    <script language="JavaScript"><!--
    for (i = 0; i < 100; ++i) {
        alert ("$gettext{'Thank you so much for visiting my homepage!'}");
    }
    //--></script>
    EOF

Only the translatable portions of the code will be extracted here, and the resulting PO file will begrudgingly improve in terms of readability.

You can interpolate hash lookups in all strings or quote-like expressions that are subject to interpolation (see the manual page `‘man perlop’` for details). Double interpolation is invalid, however:

    # TRANSLATORS: Replace "the earth" with the name of your planet.
    print gettext qq{Welcome to $gettext->{"the earth"}};

The `qq`-quoted string is recognized as an argument to `xgettext` in the first place, and checked for invalid variable interpolation. The dollar sign of hash-dereferencing will therefore terminate the parser with an “invalid interpolation” error.

It is valid to interpolate hash lookups in regular expressions:

    if ($var =~ /$gettext{"the earth"}/) {
       print gettext "Match!\n";
    }
    s/$gettext{"U. S. A."}/$gettext{"U. S. A."} $gettext{"(dial +0)"}/g;

#### 15.5.18.7 When To Use Parentheses

In Perl, parentheses around function arguments are mostly optional. `xgettext` will always assume that all recognized keywords (except for hashes and hash references) are names of properly prototyped functions, and will (hopefully) only require parentheses where Perl itself requires them. All constructs in the following example are therefore ok to use:

    print gettext ("Hello World!\n");
    print gettext "Hello World!\n";
    print dgettext ($package => "Hello World!\n");
    print dgettext $package, "Hello World!\n";

    # The "fat comma" => turns the left-hand side argument into a
    # single-quoted string!
    print dgettext smellovision => "Hello World!\n";

    # The following assignment only works with prototyped functions.
    # Otherwise, the functions will act as "greedy" list operators and
    # eat up all following arguments.
    my $anonymous_hash = {
       planet => gettext "earth",
       cakes => ngettext "one cake", "several cakes", $n,
       still => $works,
    };
    # The same without fat comma:
    my $other_hash = {
       'planet', gettext "earth",
       'cakes', ngettext "one cake", "several cakes", $n,
       'still', $works,
    };

    # Parentheses are only significant for the first argument.
    print dngettext 'package', ("one cake", "several cakes", $n), $discarded;

#### 15.5.18.8 How To Grok with Long Lines

The necessity of long messages can often lead to a cumbersome or unreadable coding style. Perl has several options that may prevent you from writing unreadable code, and `xgettext` does its best to do likewise. This is where the dot operator (the string concatenation operator) may come in handy:

    print gettext ("This is a very long"
                   . " message that is still"
                   . " readable, because"
                   . " it is split into"
                   . " multiple lines.\n");

Perl is smart enough to concatenate these constant string fragments into one long string at compile time, and so is `xgettext`. You will only find one long message in the resulting POT file.

Note that the future Perl 6 will probably use the underscore (`‘_’`) as the string concatenation operator, and the dot (`‘.’`) for dereferencing. This new syntax is not yet supported by `xgettext`.

If embedded newline characters are not an issue, or even desired, you may also insert newline characters inside quoted strings wherever you feel like it:

    print gettext ("<em>In HTML output
    embedded newlines are generally no
    problem, since adjacent whitespace
    is always rendered into a single
    space character.</em>");

You may also consider to use here documents:

    print gettext <<EOF;
    <em>In HTML output
    embedded newlines are generally no
    problem, since adjacent whitespace
    is always rendered into a single
    space character.</em>
    EOF

Please do not forget that the line breaks are real, i.e. they translate into newline characters that will consequently show up in the resulting POT file.

#### 15.5.18.9 Bugs, Pitfalls, And Things That Do Not Work

The foregoing sections should have proven that `xgettext` is quite smart in extracting translatable strings from Perl sources. Yet, some more or less exotic constructs that could be expected to work, actually do not work.

One of the more relevant limitations can be found in the implementation of variable interpolation inside quoted strings. Only simple hash lookups can be used there:

    print <<EOF;
    $gettext{"The dot operator"
              . " does not work"
              . "here!"}
    Likewise, you cannot @{[ gettext ("interpolate function calls") ]}
    inside quoted strings or quote-like expressions.
    EOF

This is valid Perl code and will actually trigger invocations of the `gettext` function at runtime. Yet, the Perl parser in `xgettext` will fail to recognize the strings. A less obvious example can be found in the interpolation of regular expressions:

    s/<!--START_OF_WEEK-->/gettext ("Sunday")/e;

The modifier `e` will cause the substitution to be interpreted as an evaluable statement. Consequently, at runtime the function `gettext()` is called, but again, the parser fails to extract the string “Sunday”. Use a temporary variable as a simple workaround if you really happen to need this feature:

    my $sunday = gettext "Sunday";
    s/<!--START_OF_WEEK-->/$sunday/;

Hash slices would also be handy but are not recognized:

    my @weekdays = @gettext{'Sunday', 'Monday', 'Tuesday', 'Wednesday',
                            'Thursday', 'Friday', 'Saturday'};
    # Or even:
    @weekdays = @gettext{qw (Sunday Monday Tuesday Wednesday Thursday
                             Friday Saturday) };

This is perfectly valid usage of the tied hash `%gettext` but the strings are not recognized and therefore will not be extracted.

Another caveat of the current version is its rudimentary support for non-ASCII characters in identifiers. You may encounter serious problems if you use identifiers with characters outside the range of 'A'-'Z', 'a'-'z', '0'-'9' and the underscore '_'.

Maybe some of these missing features will be implemented in future versions, but since you can always make do without them at minimal effort, these todos have very low priority.

A nasty problem are brace format strings that already contain braces as part of the normal text, for example the usage strings typically encountered in programs:

    die "usage: $0 {OPTIONS} FILENAME...\n";

If you want to internationalize this code with Perl brace format strings, you will run into a problem:

    die __x ("usage: {program} {OPTIONS} FILENAME...\n", program => $0);

Whereas `‘{program}’` is a placeholder, `‘{OPTIONS}’` is not and should probably be translated. Yet, there is no way to teach the Perl parser in `xgettext` to recognize the first one, and leave the other one alone.

There are two possible work-arounds for this problem. If you are sure that your program will run under Perl 5.8.0 or newer (these Perl versions handle positional parameters in `printf()`) or if you are sure that the translator will not have to reorder the arguments in her translation -- for example if you have only one brace placeholder in your string, or if it describes a syntax, like in this one --, you can mark the string as `no-perl-brace-format` and use `printf()`:

    # xgettext: no-perl-brace-format
    die sprintf ("usage: %s {OPTIONS} FILENAME...\n", $0);

If you want to use the more portable Perl brace format, you will have to do put placeholders in place of the literal braces:

    die __x ("usage: {program} {[}OPTIONS{]} FILENAME...\n",
             program => $0, '[' => '{', ']' => '}');

Perl brace format strings know no escaping mechanism. No matter how this escaping mechanism looked like, it would either give the programmer a hard time, make translating Perl brace format strings heavy-going, or result in a performance penalty at runtime, when the format directives get executed. Most of the time you will happily get along with `printf()` for this special case.

### 15.5.19 PHP Hypertext Preprocessor

RPMs
  mod_php4, mod_php4-core, phpdoc
File extension
  `php`, `php3`, `php4`
String syntax
  `"abc"`, `'abc'`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`; starting with PHP 4.2.0 also `ngettext`, `dngettext`, `dcngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  Programmer must call `setlocale (LC_ALL, "")`
Prerequisite
  ---
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  `printf "%2\$d %1\$d"`
Portability
  On platforms without gettext, the functions are not available.
po-mode marking
  ---

An example is available in the `‘examples’` directory: `hello-php`.

### 15.5.20 Pike

RPMs
  roxen
File extension
  `pike`
String syntax
  `"abc"`
gettext shorthand
  ---
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  `setlocale` function
Prerequisite
  `import Locale.Gettext;`
Use or emulate GNU gettext
  use
Extractor
  ---
Formatting with positions
  ---
Portability
  On platforms without gettext, the functions are not available.
po-mode marking
  ---

### 15.5.21 GNU Compiler Collection sources

RPMs
  gcc
File extension
  `c`, `h`.
String syntax
  `"abc"`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`, `ngettext`, `dngettext`, `dcngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  Programmer must call `setlocale (LC_ALL, "")`
Prerequisite
  `#include "intl.h"`
Use or emulate GNU gettext
  Use
Extractor
  `xgettext -k_`
Formatting with positions
  ---
Portability
  Uses autoconf macros
po-mode marking
  yes

### 15.5.22 Lua

RPMs
  lua
File extension
  `lua`
String syntax
  - `"abc"`
  - `'abc'`
  - `[[abc]]`
  - `[=[abc]=]`
  - `[==[abc]==]`
  - ...
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext.gettext`, `gettext.dgettext`, `gettext.dcgettext`, `gettext.ngettext`, `gettext.dngettext`, `gettext.dcngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  automatic
Prerequisite
  `require 'gettext'` or running lua interpreter with `-l gettext` option
Use or emulate GNU gettext
  use
Extractor
  `xgettext`
Formatting with positions
  ---
Portability
  On platforms without gettext, the functions are not available.
po-mode marking
  ---

### 15.5.23 JavaScript

RPMs
  js
File extension
  `js`
String syntax
  - `"abc"`
  - `'abc'`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`, `ngettext`, `dngettext`
textdomain
  `textdomain` function
bindtextdomain
  `bindtextdomain` function
setlocale
  automatic
Prerequisite
  ---
Use or emulate GNU gettext
  use, or emulate
Extractor
  `xgettext`
Formatting with positions
  ---
Portability
  On platforms without gettext, the functions are not available.
po-mode marking
  ---

### 15.5.24 Vala

RPMs
  vala
File extension
  `vala`
String syntax
  - `"abc"`
  - `"""abc"""`
gettext shorthand
  `_("abc")`
gettext/ngettext functions
  `gettext`, `dgettext`, `dcgettext`, `ngettext`, `dngettext`, `dpgettext`, `dpgettext2`
textdomain
  `textdomain` function, defined under the `Intl` namespace
bindtextdomain
  `bindtextdomain` function, defined under the `Intl` namespace
setlocale
  Programmer must call `Intl.setlocale (LocaleCategory.ALL, "")`
Prerequisite
  ---
Use or emulate GNU gettext
  Use
Extractor
  `xgettext`
Formatting with positions
  Same as for the C language.
Portability
  autoconf (gettext.m4) and #if ENABLE_NLS
po-mode marking
  yes

## 15.6 Internationalizable Data

Here is a list of other data formats which can be internationalized using GNU gettext.

### 15.6.1 POT - Portable Object Template

RPMs
  gettext
File extension
  `pot`, `po`
Extractor
  `xgettext`

### 15.6.2 Resource String Table

RPMs
  fpk
File extension
  `rst`
Extractor
  `xgettext`, `rstconv`

### 15.6.3 Glade - GNOME user interface description

RPMs
  glade, libglade, glade2, libglade2, intltool
File extension
  `glade`, `glade2`, `ui`
Extractor
  `xgettext`, `libglade-xgettext`, `xml-i18n-extract`, `intltool-extract`

### 15.6.4 GSettings - GNOME user configuration schema

RPMs
  glib2
File extension
  `gschema.xml`
Extractor
  `xgettext`, `intltool-extract`

### 15.6.5 AppData - freedesktop.org application description

RPMs
  appdata-tools, appstream, libappstream-glib, libappstream-glib-builder
File extension
  `appdata.xml`
Extractor
  `xgettext`, `intltool-extract`, `itstool`

### 15.6.6 Preparing Rules for XML Internationalization

Marking translatable strings in an XML file is done through a separate "rule" file, making use of the Internationalization Tag Set standard (ITS, http://www.w3.org/TR/its20/). The currently supported ITS data categories are: `‘Translate’`, `‘Localization Note’`, `‘Elements Within Text’`, and `‘Preserve Space’`. In addition to them, `xgettext` also recognizes the following extended data categories:

`‘Context’`
  This data category associates `msgctxt` to the extracted text. In the global rule, the `contextRule` element contains the following:
  - A required `selector` attribute. It contains an absolute selector that selects the nodes to which this rule applies.
  - A required `contextPointer` attribute that contains a relative selector pointing to a node that holds the `msgctxt` value.
  - An optional `textPointer` attribute that contains a relative selector pointing to a node that holds the `msgid` value.
`‘Escape Special Characters’`
  This data category indicates whether the special XML characters (`<`, `>`, `&`, `"`) are escaped with entity reference. In the global rule, the `escapeRule` element contains the following:
  - A required `selector` attribute. It contains an absolute selector that selects the nodes to which this rule applies.
  - A required `escape` attribute with the value `yes` or `no`.
`‘Extended Preserve Space’`
  This data category extends the standard `‘Preserve Space’` data category with the additional value `‘trim’`. The value means to remove the leading and trailing whitespaces of the content, but not to normalize whitespaces in the middle. In the global rule, the `preserveSpaceRule` element contains the following:
  - A required `selector` attribute. It contains an absolute selector that selects the nodes to which this rule applies.
  - A required `space` attribute with the value `default`, `preserve`, or `trim`.

All those extended data categories can only be expressed with global rules, and the rule elements have to have the `https://www.gnu.org/s/gettext/ns/its/extensions/1.0` namespace.

Given the following XML document in a file `‘messages.xml’`:

    <?xml version="1.0"?>
    <messages>
      <message>
        <p>A translatable string</p>
      </message>
      <message>
        <p translatable="no">A non-translatable string</p>
      </message>
    </messages>

To extract the first text content ("A translatable string"), but not the second ("A non-translatable string"), the following ITS rules can be used:

    <?xml version="1.0"?>
    <its:rules xmlns:its="http://www.w3.org/2005/11/its" version="1.0">
      <its:translateRule selector="/messages" translate="no"/>
      <its:translateRule selector="//message/p" translate="yes"/>

      <!-- If 'p' has an attribute 'translatable' with the value 'no', then
           the content is not translatable.  -->
      <its:translateRule selector="//message/p[@translatable = 'no']"
        translate="no"/>
    </its:rules>

`‘xgettext’` needs another file called "locating rule" to associate an ITS rule with an XML file. If the above ITS file is saved as `‘messages.its’`, the locating rule would look like:

    <?xml version="1.0"?>
    <locatingRules>
      <locatingRule name="Messages" pattern="*.xml">
        <documentRule localName="messages" target="messages.its"/>
      </locatingRule>
      <locatingRule name="Messages" pattern="*.msg" target="messages.its"/>
    </locatingRules>

The `locatingRule` element must have a `pattern` attribute, which denotes either a literal file name or a wildcard pattern of the XML file(7). The `locatingRule` element can have child `documentRule` element, which adds checks on the content of the XML file.

The first rule matches any file with the `‘.xml’` file extension, but it only applies to XML files whose root element is `‘<messages>’`.

The second rule indicates that the same ITS rule file are also applicable to any file with the `‘.msg’` file extension. The optional `name` attribute of `locatingRule` allows to choose rules by name, typically with `xgettext`'s `-L` option.

The associated ITS rule file is indicated by the `target` attribute of `locatingRule` or `documentRule`. If it is specified in a `documentRule` element, the parent `locatingRule` shouldn't have the `target` attribute.

Locating rule files must have the `‘.loc’` file extension. Both ITS rule files and locating rule files must be installed in the `‘$prefix/share/gettext/its’` directory. Once those files are properly installed, `xgettext` can extract translatable strings from the matching XML files.

#### 15.6.6.1 Two Use-cases of Translated Strings in XML

For XML, there are two use-cases of translated strings. One is the case where the translated strings are directly consumed by programs, and the other is the case where the translated strings are merged back to the original XML document. In the former case, special characters in the extracted strings shouldn't be escaped, while they should in the latter case. To control wheter to escape special characters, the `‘Escape Special Characters’` data category can be used.

To merge the translations, the `‘msgfmt’` program can be used with the option `--xml`. See section 10.1 Invoking the `msgfmt` Program, for more details about how one calls the `‘msgfmt’` program. `‘msgfmt’`'s `--xml` option doesn't perform character escaping, so translated strings can have arbitrary XML constructs, such as elements for markup.

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