We took the approach of using the natural language recognizer in the native iOS SDK to guess which language the note is in with a degree of confidence, and then passing the contents of the note and target language down to one of those services to translate. Happy to answer questions as you implement it.
Discussion
Hmm, what if the same thing is applied to global where users choose relays as is now plus what languages they want to see?
I think it could be an optional setting, with default showing everything on the Global feed. Worth exploring the idea.
If I understand this right, a client side language filter would sound interesting. I would however also like a keyword filter then, and potentially even a content blocker tie in against spam URLs.
No idea about the performance cost of such features.