Just a quick few words from my side:
I am German and quite capable of speaking (or more importantly writing) English and Dutch as well. So far, I had no problems on PL1, even with people who only understand Polish. I'm trying to do some "standard" questions in Polish (things like nowy rj? or Szlak xy dla n?), just as some other people suggested, you learn some small bits of Polish very quickly. For more complex things with people who only speak Polish (which is perfectly fine, if a similair simulator in Germany, it would also be acceptable to have some people who only spek German), I usually use a translator, which works supprisingly well.
On the other hand, many other players have been very welcoming and I had no trouble communicating with other players so far.