If you apply for a course of study taught in German, you must provide proof of being proficient in German. The relevant certificates are the DSH (German language examination for the admission of foreign students to higher education institutions) and the TestDaF (examination for German as a foreign language). Students who have passed the telc Deutsch C1 Hochschule exam (test on the German knowledge needed for success at an advanced academic level), Deutsches Sprachdiplom II (German Language Certificate) and the Goethe C2 certificate have also been accepted for admission to a German-language study course at German universities and higher-education institutions since 12 February 2016. Nevertheless, you should find out what language certificate meets the requirements of your desired course at your university.
Generally, there is no need to provide proof of German language skills for English-language study courses.