Switch language to Deutsch in The Sims 4, but the only option is English US

@will_dessi  This isn't a bug.  The English-only language-locked version of Sims 4 is supposed to be sold in the U.K., and while it's odd that you received this version from a Bulgarian copy of the game, the feature is overall working as intended.

If you can't convince EA support to give you a new serial code, which support generally doesn't do, then your only option would be to obtain a new copy of the game.  You could wait until Sims 4 becomes free to play in a couple weeks and then download it from Steam.  Your Origin-owned packs would transfer over as well; you'd just need to download them again once the Steam version was installed.  Or you could buy a physical copy or product code from a store in a location that receives the global version, for example France or Germany.  You'd still want EA support to remove your current copy before registering the new one.