Problem with letters ö,ä,à in quick buttons

[backe]

If you re on a german server letters in name titles like ö,ä,ü, are nothing unusual. Sometimes there are letters in names like à,é.
Iam playing on the german speakin Innovation server. If ive someone in my group or raid with one of this letter in his name the quick button wont work.
There s a message when you click a button. "player j□rgen could not be found" or something like that. the □ replaces one of the this letters, j□rgen = jürgen.

How can i fix this to get profit to work with all these type of letter?
It has something to do with character sets i guess.