You could help translating the user interface using Weblate, or by opening a pull request on GitHub.
If you want to add a new language, please open an issue,
or create a pull request that adds a .po file and adds the language to LINGUAS.
CI system automatically adds new strings to .pot and .po files, using
msgmerge build target. There should be no need to run it manually.
You can add/edit a .po file with the tool of your choice and create a pull
request.