Chapter 24. Internationalization and Localization

Table of Contents

gtkmm applications can easily support multiple languages, including non-European languages such as Chinese and right-to-left languages such as Arabic. An appropriately-written gtkmm application will use the appropriate language at runtime based on the user's environment.

You might not anticipate the need to support additional languages, but you can never rule it out. And it's easier to develop the application properly in the first place rather than retrofitting later.

The process of writing source code that allows for translation is called internationalization, often abbreviated to i18n. The Localization process, sometimes abbreviated as l10n, provides translated text for other languages, based on that source code.

The main activity in the internationalization process is finding strings seen by users and marking them for translation. You do not need to do it all at once - if you set up the necessary project infrastructure correctly then your application will work normally regardless of how many strings you've covered.

String literals should be typed in the source code in English, but surrounded by a macro. The gettext (or intltool) utility can then extract the marked strings for tramslation, and substitute the translated text at runtime.

Preparing your project

Note

	Note
In the instructions below we will assume that you will not be using gettext directly, but intltool, which was written specifically for `GNOME`. intltool uses `gettext()`, which extracts strings from source code, but intltool can also combine strings from other files, for example from desktop menu details, and GUI resource files such as Glade files, into standard gettext `.pot/.po` files. We also assume that you are using `./autogen.sh` from gnome-common, which, among other things, takes care of some intltool initialization.

In the instructions below we will assume that you will not be using gettext directly, but intltool, which was written specifically for GNOME. intltool uses gettext(), which extracts strings from source code, but intltool can also combine strings from other files, for example from desktop menu details, and GUI resource files such as Glade files, into standard gettext .pot/.po files. We also assume that you are using ./autogen.sh from gnome-common, which, among other things, takes care of some intltool initialization.

Create a po sub-directory in your project's root directory. Within it, create LINGUAS and POTFILES.in files, as well as a ChangeLog file so that translators can keep track of translation changes.

LINGUAS contains an alphabetically sorted list of codes identifying the languages for which your program is translated.

POTFILES.in is a list of paths to all files which contain strings marked up for translation, starting from the project root directory. So for example, the entries would look like:

      src/main.cc
      src/other.cc

If you have designed some of the application UI in Glade then also add your .glade files to the list in POTFILES.in.

Add the following code to your configure.ac, substituting 'programname' with the name of your program:

      IT_PROG_INTLTOOL([0.35.0])

      GETTEXT_PACKAGE=programname
      AC_SUBST(GETTEXT_PACKAGE)
      AC_DEFINE_UNQUOTED([GETTEXT_PACKAGE], ["$GETTEXT_PACKAGE"], [The domain to use with gettext])
      AM_GLIB_GNU_GETTEXT

      PROGRAMNAME_LOCALEDIR=[${datadir}/locale]
      AC_SUBST(PROGRAMNAME_LOCALEDIR)

This PROGRAMNAME_LOCALEDIR variable will be used later in the Makefile.am file, to define a macro that will be used in our source code, to initialize gettext.

In the top-level Makefile.am:

Add po to the SUBDIRS variable.

Define INTLTOOL_FILES as:

            INTLTOOL_FILES = intltool-extract.in intltool-merge.in intltool-update.in

Add INTLTOOL_FILES to the EXTRA_DIST list of files.

Update your DISTCLEANFILES:

            DISTCLEANFILES = ... intltool-extract intltool-merge intltool-update po/.intltool-merge-cache

In your src/Makefile.am, update your AM_CPPFLAGS:

      AM_CPPFLAGS = ... -DPROGRAMNAME_LOCALEDIR=\"${PROGRAMNAME_LOCALEDIR}\"


Using derived widgets		Marking strings for translation