Hey verse!
I am from Germany, went to school there for almost ten years..so have an idea about the whole system! One thing that German universities expect almost certainly is a certain subject combination, including Maths, a science and a foreign language next to German. In fact many German students are asked to sit a entrance test in various Universities where they have to prove their abilities in the subjects listed above. If your friend's first language is not German, he/she will have to do some entrance exams in German. However I think that an A or B at GermanA2 would be sufficient! Concerning the foreign language I am very positive that they will accept English(although it's his/her mothertongue!). Concerning the science, I hope your friend does one! If this isn't the case the best thing to do, is to write directly to the University. It may be the case that a decent grade at GCSE would be enough!
Btw, most of the informations stated above also concern Austria and Switzerland! I just wrote a letter to the admission office of the University of St Gallen, where I hope to study Management! Since I am not doing a science either, I am very curious to know their reaction and I will report back to you.
I hope this helped!