Polish is a Slavic language and is similar to other Slavic languages. Some of them are:
Russian, Belarusian and Ukrainian (of the East group)
Czech and Slovak (they are in the same West group as Polish)
Bulgarian and Macedonian (eastern dialects of the South group)
Serbo-Croatian and Slovene (western dialects of the South group)
I think that once you know Polish it may still be difficult to communicate with people who speak other Slavic languages but it will be easier to learn them.