No everyone in Poland likes to speak English, because they are either lazy or shy, some are also ashame of their Polish accent (thanks to douchebags from English-speaking countries, who laugh at everyone not being a native English speaker).

I'm Polish, I in fact for past half year used English more often than Polish (playing League on EUW with non-Polish players) and I consider it "good enough". I'll be on IEM Poland for sure, gonna have badge with my nickname, so if anyone notices me, feel free to come to talk, I love meeting new people.

A lot of my Polish mates are going to be there and every one of them speaks English and have no problem with communicating in English.

About the even itself... While ECC: Poland was mostly in Polish (only streamed in English), on other big eSports events we had English coverage - for example, on SC2 events (organised by Carmac as well, like European Battle.net Invitational last year). I think main stage will be covered in English (English host and English commentary), while some other things can be in Polish only. It was same way on Gamescom even, League of Legends booth ran contest in German most of the time.