There used to be a time when there were lots of polish players. However, it included lots of dragonarmy soldiers too, and nowadays most are gone. There is nothing wrong in talking in your own native language. And I remember something about English being the language to speak in Genesis, however if it hasn't been added in the rules section, it must have been a suggestion and not a rule.
There were a few Arkadia players that tried Genesis, too, so they were speaking in polish. Whenever I see Logg or Darkaan, Torwin or other neidar speaking in polish, I usually tease them mumbling "mountain dwarf language", so they switch back to English immediately
