Simple, only answer in english.
Anyway, in germany it's law that IFR RT hast to be provided in english, for VFR german is allowed. I guess it is pretty similar in scandinavia, always a pleasure to fly there with very friendly and professional service.
I know the DFS took some already licensed ATCOs in during the last few years, if i remember it correctly it was mentioned in "transmission" that those that didn't speak german were limited to upper airspace only until they learned enough german.