Cant't find words containing "Umlaut"-character

Helllo

in my case pdf documents are indexed by swish-2. The used language german contains characters like Umlaute (ä ö ü Ä Ö Ü) and ß.
As you can see from the attached screen shots, the named characters are not displayed correctly. It is also not possible to search for words containing one of these characters.

Regards
Schildi