i'm working with several Polish people here in France and they all discourage me from learning it
Do not listen to them. They're either stupid or want your time in Poland to be far worse than it has to be.
For your question. Many, many people have taken English classes at some time, but many people who have are shy about using it or haven't learned enough to understand a native in real time or didn't really try to learn much.
Younger people in cities are more likely to have learned some, but it's not something you can (or should) ever really depend upon.
And the difficulty isn't quite as bad as cracked up to be. No, it's not easy, but you can get basic functional ability (which does not depend upon being perfect) in a couple of months here if you apply yourself.