As a former American exchange student to Germany, the best advice I got back then was to repeat to anyone constantly answering you in English (after you've tried your best to speak German) that the reason you came to Germany was to learn German. Note Germans are not always being condescending when they reply in English: in many cases, they may not have spoken any English in weeks or months and are just happy at the chance to use some knowledge of what they learned in school.
Side note: during my exchange year, it hardly happened to me at all because I'd worked so much on my pronunciation beforehand- yes, people thought I was a lot better than I was (in the beginning I could hardly understand anything due to the speed of everyday talking). It certainly helps if you pay attention to your pronunciation.