[Otter74]

legion's suggestion is the best one. I think "where did you learn to speak English?" is not necessarily appropriate because it implies that English is not a native language of the speaker, which is not necessarily the case even when you think it might be. (E.g. one of my best friends is from Bangalore and English is actually her first language, ahead of Kanada and Hindi.) I find "where are you from?" to be a problematic question; I could give at least three possible answers to that question. One of the most unusual accents I've heard (in English) was from a woman from Barcelona whose parents were from Jackson, TN - it was a mix of Spanish-accented English and west Tennessee English.