Now that you've learned about Meson, the next step is to make your app able to be translated to different languages. The first thing you need to know is how to convert strings in your code into translatable strings. Here's an example:

stdout.printf ("Not Translatable string");
stdout.printf (_("Translatable string!"));
​
string normal = "Another non-translatable string";
string translated = _("Another translatable string");

See the difference? We just added _() around the string! Well, that was easy! Go back to your project and make all your strings translatable by adding _().

Now we have to make some changes to our Meson build system and add a couple new files to describe which files we want to translate and which languages we want to translate into.

1. Open up your "meson.build" file and add these lines below your project declaration:

   # Include the translations module
   i18n = import('i18n')
   ​
   # Set our translation domain
   add_global_arguments('-DGETTEXT_PACKAGE="@0@"'.format (meson.project_name()), language:'c')

2. Remove the lines that install your .desktop and appdata files and replace them with the following:

   #Translate and install our .desktop file
   i18n.merge_file(
       input: join_paths('data', 'hello-again.desktop.in'),
       output: meson.project_name() + '.desktop',
       po_dir: join_paths(meson.source_root(), 'po'),
       type: 'desktop',
       install: true,
       install_dir: join_paths(get_option('datadir'), 'applications')
   )
   ​
   #Translate and install our .appdata file
   i18n.merge_file(
       input: join_paths('data', 'hello-again.appdata.xml.in'),
       output: meson.project_name() + '.appdata.xml',
       po_dir: join_paths(meson.source_root(), 'po'),
       install: true,
       install_dir: join_paths(get_option('datadir'), 'metainfo')
   )

   The merge_file method combines translating and installing files, similarly to how the executable method combines building and installing your app. You might have noticed that this method has both an input argument and an output argument. We can use this instead of the rename argument from the install_data method.

3. Still in this file, add the following as the last line:

   subdir('po')

4. You might have noticed in step 2 that the merge_file method has an input and output. We're going to append the additional extension .in to our .desktop and .appdata.xml files so that this method can take the untranslated files and produce translated files with the correct names.

   git mv data/hello-again.desktop data/hello-again.desktop.in
   git mv data/hello-again.appdata.xml data/hello-again.appdata.xml.in

   We use the git mv command here instead of renaming in the file manager or with mv so that git can keep track of the file rename as part of our revision history.

5. Now, Create a directory named "po" in the root folder of your project. Inside of your po directory you will need to create another "meson.build" file. This time, its contents will be:

    i18n.gettext(meson.project_name(),
        args: '--directory=' + meson.source_root(),
        preset: 'glib'
    )

6. Inside of "po" create another file called "POTFILES" that will contain paths to all of the files you want to translate. For us, this looks like:

   src/Application.vala
   data/hello-again.desktop.in
   data/hello-again.appdata.xml.in

7. We have one more file to create in the "po" directory. This file will be named "LINGUAS" and it should contain the two-letter language codes for all languages you want to provide translations for. As an example, let's add German and Spanish

   de
   es

8. Now it's time to go back to your build directory and generate some new files using Terminal! The first one is our translation template or .pot file:

   ninja com.github.yourusername.yourrepositoryname-pot

   After running this command you should notice a new file in the po directory containing all of the translatable strings for your app.

9. Now we can use this template file to generate translation files for each of the languages we listed in the LINGUAS file with the following command:

   ninja com.github.yourusername.yourrepositoryname-update-po

   You should notice two new files in your po directory called de.po and es.po. These files are now ready for translaters to localize your app!

10. Last step. Don't forget to add all of the new files we created in the po directory to git:

    git add src/Application.vala meson.build po/ data/
    git commit -am "Add translations"
    git push

That's it! Your app is now fully ready to be translated. Remember that each time you add new translatable strings or change old ones, you should regenerate your .pot and po files using the -pot and -update-po build targets from the previous two steps. If you want to support more languages, just list them in the LINGUAS file and generate the new po file with the -update-potarget. Don't forget to add any new po files to git!

Translators Comments

Sometimes detailed descriptions in the context of translatable strings are necessary for disambiguation or to help in the creation of accurate translations. For these situations use /// TRANSLATORS: comments.

/// TRANSLATORS: The first %s is search term, the second is the name of default browser
title = _("Search for %s in %s").printf (query, get_default_browser_name ());