Please consider that the tuition language is not uniform. In core elective modules the language will be English if there is at least one foreign student present. Some elective modules may be German only. Modules of the bachelor program are always in German. In the labs you will here a lot of languages, but English is always OK. We expect that you learn a little bit German during your studies - maybe at the end you are capable also to participate in a German lecture. The language of the master thesis may be either English or German.
You may get a general impression how to undertake a study program at a German university by reading the information given by the INOBIS-Website or by the "Deutsches Studentenwerk".