Sometimes it does feel like studing not in Germany, but US.
You study in English. Though most bachelor programmes are thought in German, at master's level degree more and more courses are being offered in English.
You speak English. Here at the University of Heidelberg, more than 20% percent of the students come from foreign countries and for many, English, not German, is the first foreign language. Because of that, you mostly speak English when you go out in a group as there are some that do not speak German.