I have no statistics, but I would say that 3/4 have German and English RT. It is written on the Jeppesen/Bottlang charts what languages are spoken. And every airfield/airport with a control zone or class F airspace must provide English RT.
They are usually able, sometimes required, to speak English *to you*. But the rest of the circuit traffic may be talking in German. And even en-route Langen Info & similar will speak German with the German traffic.
Having a rudimentary understanding of German, and a crib sheet with the common phrases in the circuit may help a lot with your situational awareness. And if you can say "Guten Tag" and "Auf Wiedersehen", so much better. Even if the rest of your RT is in English.