No. Many are, especially higher level courses (ie, above the Bachelor level), but not nearly all of them. Some lecturers try to hold their lectures in English

No. Many are, especially higher level courses (ie, above the Bachelor level), but not nearly all of them. Some lecturers try to hold their lectures in English even though they speak it very poorly. Pretty much all lecturers will happily take English questions and answer them in English. And all German comp sci students speak English. For many courses which are held in German the materials are still in (some kind of) English. You can usually get by very, very well by skipping the classes entirely and learning from the provided materials only. In fact, that's what a large number of German students are doing too.