The English language skills of at least level B2 (GeR) are most easily demonstrated by a German high school diploma certificate (Abiturzeugnis), if it shows that at least six years of English have been completed. Alternatively, you may submit a bachelor's or bachelor's degree certificate of the first professional qualification (Bachelor's degree) obtained in an English-speaking country (eg USA, UK, Australia, New Zealand, Canada or Ireland). Another proof could be a final certificate of the first professional qualification (Bachelor), whose language was English (all modules have to be fully taught in English - proof is required!).
In addition, your English knowledge can be demonstrated by various test results.
Other than the listed references cannot be recognized. A DAAD language certificate is not a recognized English tests! A confirmation of the university or participation in English courses is not sufficient as proof!
Advanced English knowledge is not only necessary because of the foreign semester, but also because the most important scientific essays, of which many are to be read during the course of studies, appear in English-language journals.