the creation of a new group does now allow German letters (umlauts) like ä, ö, ü and ß
But it is not mentioned in the error message that only ANSI letters are allowed.
Would be good to mention it in the error message that only ANSI is allowed in the group names.
「いいね！」 1
Group names follow the same rules as usernames. The username error also does not mention ASCII only. Username must only include numbers, letters, dashes, and underscores.
I’m not sure if adding “ASCII” to the error would be a good idea, however, as most users won’t know that is.
「いいね！」 2
ä, ö, ü, and ß are letters.
What is the technical reason why they are not allowed?
Unfortunately regular users usually do not know about ASCII, ANSI and such things. You are welcome to update the German translation of that error message on Transifex to make it easier for German speaking people to understand.
I really hope that we can lift the ASCII restriction for usernames and group names sometime in the future, but yeah, we have to live with it for now. Sorry about that.
「いいね！」 5
I did there already a couple of the german translations for Discourse in the last couple of months. 
I will have a look at this specific error message on the weekend.
「いいね！」 2
Unicode ユーザー名とグループ名は、すでに長い間サポートされています。「Unicode ユーザー名」のサイト設定を有効にしてください。
「いいね！」 4
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