GOG Users pay the very same price for the game, so there is no valid reason why they should receive the version of less features/languages/... I think you would agree on that, wouldn't you?
Why should GOG as platform refuse to get more languages for a game they distribute?
Why should Kalypso as publisher remove individual languages just because of another website selling the game?
And if there would be any issue with selected languages being blocked on GOG, that would be up on GOGs side, but there are plenty of games with Chinese language here.
So please adapt the GOG version to the Steam version and stop treating GOG users as 2nd class customers that only receive a worse version of the game.