I am a native Norwegian, and speak quite good German (not entirely fluent, having never lived for an extended period in any German-langauge country), but with a slight Norwegian accent.

Germans tend to be satisfied that I speak German, but in Munich they have always (i.e. since the mid-eighties for me) tended to switch to English at the first whiff of a non-German accent. This tendency tends to spread to other parts of Germany, as well. Especially Berlin, where five years ago one would still find people in gastronomy not speaking English, is now nearly as bad as Munich.

A gentle reminder that there is no need for both parties in the conversation to speak a foreign langauge usually does the trick, though. The very few still impolite enough to address me in English, with me still speaking German, usually speak far worse English than my German!