In the eastern part, at least, I heard you could get by surprisingly well if you only know Polish and English.
The only times I was in Germany itself was when travelling to some other country (Switzerland, France, or returning to Poland from Denmark), so I haven't had much experience with it, but it does seem that English alone is insufficient even in places like McCafe next to a highway. I managed to place an order with the help of the guide, but it wasn't very easy and involved lots of loud, slow speech and pointing at signs above the counter.
That said, from what I've seen of German physics students, they seem to know English quite well (it's pretty much a given if you want to go anywhere in this field, scientific papers in general aren't translated too often).
