There isn't a lot of teaching involved for PhDs at most German universities. Most simply require that you write the dissertation and come in for a talk about it at the end. A few also require you to take some courses, but mostly, it is just your own research that you are doing. And you could do that from Russia I guess. Depends on the supervisor as well, I would say. Any way, I think you have far more choices than the university in Hagen. English mostly isn't a problem; however, you'd better check with the respective university for that.
I would advise to find out what you would like to do research on and then find an appropriate supervisor.