As soon as you give your passport to the officer, he/she will know whether you are a German citizen or not. If you are a non-EU/EFTA citizen and on the right queue, the officer doesn't need your passport either to start talking in English.
The questions generally include the following topics:
Purpose of your visit
Duration of your stay
Your return ticket
Your travels to other places (during your stay in the Schengen Area)
I had about 10 visits to Germany, two of them were to Frankfurt, I have never got a question in German from the officers. Maybe I said "danke" at the end of the conversation, that's all.