Well I wouldn't like to see this forum to turn into a multilingual mess. It's counterproductive if you want to help or contribute to a discussion but do not know the language the people in that particular thread speak. I can speak three languages myself, including German, but I'd appreciate if the community of this forums would stick to the international language. 
That said, speaking in a different language is not banned here, but I guess it's fair if we kindly advertise that English is still preferred. However I only speak for myself.