Huh. Well, the fact is, language moves and changes. I don't use jumper to mean sweater, but I would use flat to mean apartment (and do). Unless it's actually confusing or really stands out (as with a man in a pregnant-looking dress), I shouldn't think it's that big an issue.
Or, I suppose, there's an absolute threshold below which dialect and variant vocabulary are not noticeable to me, and then above that threshold it's a game of "cosmopolitan, ignorant, or trying too hard?"
Whereas more than 2-3 words in a foreign language automatically qualify as "trying too hard", for me, and that goes double on TV, and that goes triple when the TV actors don't actually speak that language. (Bad Firefly! Alias gets a pass only because (a) Vaughn is French and (b) they sometimes use subtitles.) Foreign words with translation -- trying too hard but at least concerned about the reader; foreign words without translation -- probably the author is being snotty. Heaven knows, I have been snotty, but that does nto stop me from hating it in other people.