Can't change language

I can't change language from Polish to anything else. I right-click MudRunner in the Library, choose Properties, but the Language tab isn't there. I have a retail version, physical disc.

Hi, games stuck in polish are usually because the Steam key has been purchased on key seller websites. Where did you buy the game?

I ordered physical disc on
What puzzles me, why does everyone get every language, yet Poland only gets Polish?
Even the original Spintires from the same retailer has all the languages on the cd. Why is Mudrunner different?

That's because, sadly, a lot of polish keys are sold on key seller websites. Because the price in the country is relatively low, it's attractive for these websites to buy many polish keys and sell them in other countries at a higher price.

Polish keys are often locked in polish language to counter this.