Localization using gettext

In addition to Importing translations in CSV format, Rebel Engine also supports loading translation files written in the GNU gettext (.po) format.

Note

For an introduction to gettext, check out A Quick Gettext Tutorial. It's written with C projects in mind, but much of the advice also applies to Rebel Engine (with the exception of xgettext).

Advantages

  • gettext is a standard format, which can be edited using any text editor or GUI editors such as Poedit.

  • gettext is supported by translation platforms such as Transifex and Weblate, which makes it easier for people to collaborate to localization.

  • Compared to CSV, gettext works better with version control systems like Git, as each locale has its own messages file.

  • Multiline strings are more convenient to edit in gettext files compared to CSV files.

Disadvantages

  • gettext is a more complex format than CSV and can be harder to grasp for people new to software localization.

  • People who maintain localization files will have to install gettext tools on their system. However, as Rebel Engine doesn't use compiled message object files (.mo), translators can test their work without having to install gettext tools.

Caveats

  • As Rebel Engine uses its own PO file parser behind the scenes (which is more limited than the reference GNU gettext implementation), some features such as pluralization aren't supported.

Installing gettext tools

The command line gettext tools are required to perform maintenance operations, such as updating message files. Therefore, it's strongly recommended to install them.

  • Windows: Download an installer from this page. Any architecture and binary type (shared or static) works; if in doubt, choose the 64-bit static installer.

  • macOS: Install gettext either using Homebrew with the brew install gettext command, or using MacPorts with the sudo port install gettext command.

  • Linux: On most distributions, install the gettext package from your distribution's package manager.

Creating the PO template (POT) manually

Rebel Engine currently doesn't support extracting source strings using xgettext, so the .pot file must be created manually. This file can be placed anywhere in the project directory, but it's recommended to keep it in a subdirectory, as each locale will be defined in its own file.

Create a directory named locale in the project directory. In this directory, save a file named messages.pot with the following contents:

# Don't remove the two lines below, they're required for gettext to work correctly.
msgid ""
msgstr ""

msgid "Hello world!"
msgstr ""

Messages in gettext are made of msgid and msgstr pairs. msgid is the source string (usually in English), msgstr will be the translated string.

The msgstr value in PO template files (.pot) should always be empty. Localization will be done in the generated .po files instead.

Creating the PO template (POT)

Creating a messages file from a PO template

The msginit command is used to turn a PO template into a messages file. For instance, to create a French localization file, use the following command while in the locale directory:

msginit --no-translator --input=messages.pot --locale=fr

The command above will create a file named fr.po in the same directory as the PO template.

Alternatively, you can do that graphically using Poedit, or by uploading the POT file to your web platform of choice.

Loading a messages file in Rebel Editor

To register a messages file as a translation in a project, open the Project Settings, then go to the Localization tab. In Translations, click Add… then choose the .po file in the file dialog. The locale will be inferred from the "Language: <code>\n" property in the messages file.

Note

See Internationalizing games for more information on importing and testing translations in Rebel Editor.

Updating message files to follow the PO template

After updating the PO template, you will have to update message files so that they contain new strings, while removing strings that are no longer present in the PO template. This can be done automatically using the msgmerge tool:

# The order matters: specify the message file *then* the PO template!
msgmerge --update --backup=none fr.po messages.pot

If you want to keep a backup of the original message file (which would be saved as fr.po~ in this example), remove the --backup=none argument.

Note

After running msgmerge, strings which were modified in the source language will have a "fuzzy" comment added before them in the .po file. This comment denotes that the translation should be updated to match the new source string, as the translation will most likely be inaccurate until it's updated.

Strings with "fuzzy" comments will not be read by Rebel Engine until the translation is updated and the "fuzzy" comment is removed.

Checking the validity of a PO file or template

It is possible to check whether a gettext file's syntax is valid by running the command below:

msgfmt fr.po --check

If there are syntax errors or warnings, they will be displayed in the console. Otherwise, msgfmt won't output anything.