Prerequisites

Simple project Let's start with some simple project, the "Hello world" program for example /* hello.c */ #include <stdio.h> int main(int argc, char* argv[]) { printf("Hello world\n"); return 0; } Prepare simple SConstruct script to compile the program. # SConstruct env = Environment() hello = Program(["hello.c"]) Now we'll convert the project to multi-lingual one. I assume, that you already have GNU gettext utilities installed. If not, install it from repository, or download from http://ftp.gnu.org/gnu/gettext/. For the purpose of this example, you should have following three locales installed on your system en_US, de_DE and pl_PL. On debian, for example, you may enable certain locales through dpkg-reconfigure locales. We first prepare the hello.c program, for internationalization. Change the previous code so it reads as follows: /* hello.c */ #include <stdio.h> #include <libintl.h> #include <locale.h> int main(int argc, char* argv[]) { bindtextdomain("hello", "locale"); setlocale(LC_ALL, ""); textdomain("hello"); printf(gettext("Hello world\n")); return 0; } This way we prepared source code. Detailed recipes for such preparation can be found at http://www.gnu.org/software/gettext/manual/gettext.html#Sources. The gettext("...") in above source has two purposes. First is is recognized by the xgettext(1) program, which we will use to extract from the sources the messages for localization. Second, it calls the gettext library internals to translate the message at runtime. Now we shall instruct SCons how to generate and maintain translation files. For that, we use &b-link-Translate; builder and &b-link-MOFiles; builder. First one takes a couple of source files, extracts internationalized messages from them, creates so-called POT file (translation template), and then creates PO translation files, one for each requested language. Later, during the development lifecycle, the builder keeps all these files up-to date. The &b-link-MOFiles; builder compiles the PO files to binary form. After all, we install the MO files under directory called locale. The complete code of SConstruct script for multi-lingual "Hello world" will be following: # SConstruct env = Environment( tools = ['default', 'gettext'] ) hello = env.Program(["hello.c"]) env['XGETTEXTFLAGS'] = [ '--package-name=%s' % 'hello', '--package-version=%s' % '1.0', ] po = env.Translate(["pl","en", "de"], ["hello.c"], POAUTOINIT = 1) mo = env.MOFiles(po) InstallAs(["locale/en/LC_MESSAGES/hello.mo"], ["en.mo"]) InstallAs(["locale/pl/LC_MESSAGES/hello.mo"], ["pl.mo"]) InstallAs(["locale/de/LC_MESSAGES/hello.mo"], ["de.mo"]) Generate translation files with scons po-update. You should see the output from SCons simillar to this: ptomulik@:$ scons po-update scons: Reading SConscript files ... scons: done reading SConscript files. scons: Building targets ... Entering '/home/ptomulik/projects/tmp' xgettext --package-name=hello --package-version=1.0 -o - hello.c Leaving '/home/ptomulik/projects/tmp' Writting 'messages.pot' (new file) msginit --no-translator -l pl -i messages.pot -o pl.po Created pl.po. msginit --no-translator -l en -i messages.pot -o en.po Created en.po. msginit --no-translator -l de -i messages.pot -o de.po Created de.po. scons: done building targets. If everything is right, you shall see following new files. ptomulik@:$ ls *.po* de.po en.po messages.pot pl.po Open en.po in poedit and provide english "translation" to message "Hello world\n". Do the same for de.po (deutsch) and pl.po (polish). Let the translations be, for example: en: "Welcome to beautiful world!\n" de: "Hallo Welt!\n" pl: "Witaj swiecie!\n" Now compile the project by executing scons command. The output should be similar to this: ptomulik@:$ scons scons: Reading SConscript files ... scons: done reading SConscript files. scons: Building targets ... msgfmt -c -o de.mo de.po msgfmt -c -o en.mo en.po gcc -o hello.o -c hello.c gcc -o hello hello.o Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo" Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo" msgfmt -c -o pl.mo pl.po Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo" scons: done building targets. SCons automatically compiled PO files to binary format MO, and the InstallAs lines installed these files under locale folder. Your program should be now ready. You may try it as follows (linux): ptomulik@:$ LANG=en_US.UTF-8 ./hello Welcome to beautiful world ptomulik@:$ LANG=de_DE.UTF-8 ./hello Hallo Welt ptomulik@:$ LANG=pl_PL.UTF-8 ./hello Witaj swiecie To demonstrate further life of translation files, let's change polish translation (poedit pl.po) to "Witaj drogi swiecie\n". Run scons to see how scons reacts to this ptomulik@:$scons scons: Reading SConscript files ... scons: done reading SConscript files. scons: Building targets ... msgfmt -c -o pl.mo pl.po Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo" scons: done building targets. Now, open hello.c and add another one printf line with new message. /* hello.c */ #include <stdio.h> #include <libintl.h> #include <locale.h> int main(int argc, char* argv[]) { bindtextdomain("hello", "locale"); setlocale(LC_ALL, ""); textdomain("hello"); printf(gettext("Hello world\n")); printf(gettext("and good bye\n")); return 0; } Compile project with scons. This time, the msgmerge(1) program is used by SCons to update PO file. The output from compilation is like: ptomulik@:$scons scons: Reading SConscript files ... scons: done reading SConscript files. scons: Building targets ... Entering '/home/ptomulik/projects/tmp' xgettext --package-name=hello --package-version=1.0 -o - hello.c Leaving '/home/ptomulik/projects/tmp' Writting 'messages.pot' (messages in file were outdated) msgmerge --update de.po messages.pot ... done. msgfmt -c -o de.mo de.po msgmerge --update en.po messages.pot ... done. msgfmt -c -o en.mo en.po gcc -o hello.o -c hello.c gcc -o hello hello.o Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo" Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo" msgmerge --update pl.po messages.pot ... done. msgfmt -c -o pl.mo pl.po Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo" scons: done building targets. The last example demonstrates what happens, if we change the source code in such way, that the internationalized messages do not change. The answer is, that none of translation files (POT, PO) is touched (i.e. no content changes, no creation/modification time changed and so on). Let's append another one instruction to the program (after the last printf), so its code becomes: /* hello.c */ #include <stdio.h> #include <libintl.h> #include <locale.h> int main(int argc, char* argv[]) { bindtextdomain("hello", "locale"); setlocale(LC_ALL, ""); textdomain("hello"); printf(gettext("Hello world\n")); printf(gettext("and good bye\n")); printf("----------------\n"); return a; } Compile project. You'll see on your screen ptomulik@:$scons scons: Reading SConscript files ... scons: done reading SConscript files. scons: Building targets ... Entering '/home/ptomulik/projects/tmp' xgettext --package-name=hello --package-version=1.0 -o - hello.c Leaving '/home/ptomulik/projects/tmp' Not writting 'messages.pot' (messages in file found to be up-to-date) gcc -o hello.o -c hello.c gcc -o hello hello.o scons: done building targets. As you see, the internationalized messages ditn't change, so the POT and the rest of translation files have not even been touched.