This question just kind of popped into my head, so I'm not sure whether it is really a good question for this site, but I wonder if anybody has written about it. I would imagine that since when ...
(Inspired by this comment). Does halacha permit Jews to speak languages other than Hebrew? Bedieved? Lechatchilah?
I've heard the slang "he bageled me" meaning "he identified me as a fellow Jew (even though it wasn't obviously apparent)." There are the times I pass someone in the street who's wearing a baseball ...