The broken English I've written for hockey has been based pretty much entirely on watching a lot of interviews of the players in question. Malkin has some particular tics that he uses, whereas Ovechkin is more fluent but also has some phrases that he likes, etc.

I haven't done a lot with people hearing languages they don't know, though. Once when I did, I just described what the POV character was hearing - they couldn't understand it, so it wouldn't have been fair for the reader to (unless we're going for dramatic irony of course). I realize that's a fairly basic solution, though, which I am sure you've used in the past!