Geoff Pullum has a Lingua Franca piece about an odd phenomenon he’s run across: people who get offended if you try to converse in their own language. Only two examples, mind you—an English-speaking American, fluent in German, whose German university colleagues don’t want him to speak German with them and a native speaker of English who “has learned Korean really well,” but encounters hostility when he uses it to talk to students and colleagues, who “seem to think it is distasteful that he should do such a thing”—but he’s not claiming it’s representative, just surprising:
I had of course seen this kind of reluctance to let outsiders join the speech community with languages of very low prestige, for instance creole languages. Efforts at learning Jamaican Creole are typically met with anger rather than pleasure in Jamaica: Jamaicans, especially if middle-class or college-educated, want to be regarded as English speakers. They tend to despise the creole that is in fact the primary medium of oral communication across the country.
But discouragement from learning prestigious national languages like Berlin German and Seoul Korean? It amazed me.
The comment thread is worth reading as well.