I just started step aerobics classes in one of the migros fitness parks. Ok, german is not such a problem for me, but the way the classes are there is really no need to be perfect in German, its all about right moves and repeat after the instructor.
Could be a bit different for youga and pilates as there I think it's important to understand the instructions to follow them in a correct way. But then again it's a nice way to pick up the language
Good luck !