To contribute translations, sign up at Transifex. Joining a team for an existing language is automatic. New languages unfortunately need to be approved; I try to get these done within 24 hours. When picking a new language, I recommend going for the more general dialect unless the difference is essential; i.e. chose
Danish (Denmark) and similar.
A while ago someone proposed that the Syncthing UI should be translated to other languages. I kind of shot it down because I thought things were changing too fast for it to be practical. I’m reconsidering that. If I were to set up a project on Transifex, are there people interested in helping out translating the GUI to their native language? The base language would be English, I myself can contribute Swedish.
(There’s some scaffolding required to accomplish this, apart from the whole transifex thing; basically extracting all language strings and rebuilding the UI to be language aware.)