Why can't players from certain countries change their game language?

I mean we can change our game language, but Czech, Russian and Polish are the only languages we can choose from. 

Some time ago I heard that it's all about the price of the game and packs, but recently I checked and the pricing seems pretty much the same (e.g. expansion packs are slightly cheaper in PLN than USD, but stuff packs are more expensive), except for the fact that (at least in Poland) it's in PLN.

I really wish I could change the language to English since it's the only language I use online. It's just really frustrating that I can't do that and I'd love to know why it is so (and if possible, know how to change my game language without buying a new version of the game and all of the packs).