I don't exactly know where they get the translation model from (the source I've found has fewer languages). You can find a barebones translation UI at about:translations in FF.
I don't know how well will it work at generating non-weird-sounding German; I only ever used it to translate from languages I speak less than French for my own understanding and it produced somewhat clunky output (but IIRC mostly when it changed meaning in some pretty guessable way).
@robryk Nice! It’s clearly really bad for anything public-facing (I can tell after just putting in one test sentence), but absolutely perfect for my use, thanks!
@robryk What is “the thing firefox uses”?
My usecase is usually “write something in English and get it vaguely translated into German, whence I rewrite parts of it, ‘cause I don’t like the translator’s style”, so anything spitting out mostly correct German should be fine.