To study in Germany, you need to prove that you speak English or German well enough to study in that language. This proof needs to be delivered by handing in an official language certificate unless you are a native speaker or have graduated from an English or German-speaking program.
More than 245,000 international students are currently enrolled at German universities, most of them come from non-English and non-German speaking countries. Therefore, universities are prepared to have second-language speakers in the classroom.
As a rule of thumb, German universities require you to present a proof of upper intermediate to advanced German language skills (level B2/C1) to study in German. You can prove your German level with TestDaF, Goethe or alternative certificates to get admitted to a degree program in Germany.