I think i have found my problem.
I changed my CharsetFilter-Class, getting the File-Ending of the ServletPath and checking if the ending is jsp or jsf. Only in this case, i set the contenttype and the characterencoding.
I don't know, if this is the best solution, but for the time, it works for my application.
Maybe i will find a better solution in the future!
Be sure, Ajax4jsf is a first filter registered in the web.xml
Yes, ajax4jsf-Filter is the first configured filter in my web.xml