The game's launcher allows to choose game's language. After selecting Polish in both sections (audio and text) game still is in full English. Have you experienced this issue?

BTW I don't mind playing in English, it's more about my curiosity ;-)

Sometimes gog provides different installers for different language versions, or additional installers for other language packs.

That's correct, but this isn't such case.

There is an option in the in-game menù.

Change it in-game. The launcher tends to reset the settings to defaults f*** know why. BTW I think polish voiceover is one of a few bad things I can say about this game. Well, at least in the begining It's terrible so I switched to english right after the first murder scene. :/

To avoid reset don't start the game by the launcher but directly the AstronautsGame-Win64-Shipping.exe.

Thanks for the info guys :>