SUMO uses the gettext tooling to maintain a list of translated strings. The main work of translation is done by the community using Weblate. Every change at Weblate creates a commit into their clone of the SUMO repository which will be merged (currently manually) into the main line after review. The weblate repository gets updated automatically by a webhook installed by Eclipse at the main repo.

So if you want to add translation strings open an account at Weblate and start.

Marking translatable strings#

In the code every string which needs translation should be marked with the TL macro like this: TL("String to be translated"). We decided against the often used _ macro for readability.

The macro is defined in src/utils/common/MsgHandler.h which needs to be included (but often already is). If you have strings which are concatenated using + you should replace them using the TLF macro like TLF("The vehicle '%' has a message.", id) or one of the formatting versions of our WRITE_MESSAGE macros. So instead of WRITE_MESSAGE("The vehicle '" + id "' has a problem."); use WRITE_MESSAGEF(TL("The vehicle '%' has a problem."), id); (this works for WRITE_WARNING and WRITE_ERROR as well).

Please be aware that changing a translatable string in the code (even if you just fix a typo) will invalidate (i.e. remove) all translations. This does not mean you should not do it, you should just review the changes to the translation files as well.

Using translations#

Until we have a sufficient amount of translated strings the translations are disabled by default. If you want to activate them nevertheless, you need to make sure the gettext tools and internationalization library are installed. For Windows we have them in the SUMOLibraries, for Linux they are probably already installed, if not use the equivalent of sudo apt install gettext on your system.

The translation strings are split into two files for each language residing in $SUMO_HOME/data/po, one for GUI stuff and one for the command line applications. While it is possible to edit these files directly, it is discouraged to avoid merge conflicts with the Weblate translations. These files still need to be compiled to be usable. Currently this is done manually by calling tools/build/ This script also does a full scan of the src dir and checks for new translatable strings. If it finds some, all existing po files will be updated accordingly.

New language#

If you want to add a new language either open an issue with your request or run tools/build/ -l <lang> and make a pull request with the resulting po files.