I think there are two perspectives here.
First is this game is run by a German company. As players, we sign up with an understanding that they have clear rules, and if that rule includes a language limitation for various reasons, we just have to accept that.
Secondly, this game has been advertised throughout the world. Initially Bigpoint advertised it, and even though they don't run it anymore, the clear business objective of the game is to attract players from all around the world. If the owners of the game want that, they also need to evaluate how to handle the language complications. A baseline needs to be that a game with international objectives needs to clarify what the objectives are. Is there a need/desire to favor German players? If not, then why accept one localized language (German) along with the statement that English is representative of all the other players from other countries... It just seems like the business model is not clearly established.
Is this a local game for German language speakers? Or is this an international game? It shouldn't reasonably be both.
But again, I signed up clearly aware that German and English are the limits, so I will respect the rules.