I do think this would be easiest (and possible to be done) server side only. If the server can see the lang var on the client then great, otherwise it could even be done via a variety of kludges (set first character of nickname to a single letter language code, etc.). OR... the google api actually offers an "auto", where it attempts to figure out what the source language is. I've never seen it guess wrong, but who knows.
If for some reason its determined to be best to offload translation calls to the client.... just have the reborn client patch do it, no server changes needed.
And net traffic could even be further reduced if you implement a limited (tunable max values and deletes for unused after x minutes or hours) mem res cache, maybe even pre-seeded with likely translations per language. I am sure that "good game", "nice shot", "how you doing" - would make a big chunk of traffic unnecessary.
https://github.com/matheuss/google-translate-api
And somewhere.... I have seen one page with examples of calling the api in like 10 or more programming faiths....
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