Historically, Galette was available in English and French. A Spanish version did exists from a while, but it was not maintained and has been retired. A German version has been added more recently (which is also a little outdated today, unfortunately)...
I've recently decided to migrate Galette translations on a collaborative web platform, based on Weblate software. New languages have been added and integrated into Galette :)
From now on all translations will be integrated in releases and in development version as it arises, whatever their advancement is. Galette languages management has been reworked to include and propose all languages to users.
In the future, I'll try to add documentation translation and official plugins.
No longer hesitate, join the community and help translating Galette!