so we have english discord, forums, rules, patch notes, server, etc... but that doesnt really matter and here is why:
imagine, for a second: your whole game is in german. that means german text and german voice! Now imagine they have a question and ask in chat ... of course they ask in german. who could blame them?
How many people are active in the forums/discord? lets say 10% (and that's probably WAY too generous), that means 90% of people only ever come here to download the game once and then just play. So they only experience german for the majority of their time ingame and also ignore chat most of the time. You can counter that only by deleting all but the english client.
in my opinion it makes sense to make an extra german channel.... give it another color and offer the chance to leave it and everything is fine. you gotta moderate that ...sure but you also have to moderate the content if they talk in beginner/global/trade/LFG, so there is not more content to moderate, just another color in your chat!
for the "don't split the community, speak english like we all do" comment: the community is already split, through the language barrier. so might as well give them a different color
you probably dont know any other languages other than english, right? it's the same for many german speaking people. they dont have to use english at all if they don't want to most of the time in their life. EVERYTHING is translated to german. be it movies, user manuals, comics, whatever.
Also if people are looking for a group in german, they will prefer germans anyway - no matter which channel they use to find each other.