Hi Gunnar,
We do not have any translations yet for the Staff Directory. If you want to help make one, that would be great!
To do it, you need to get the locallang.xml file from typo3conf/ext/wecstaffdirectory/pi1 folder. Then you need to copy all that is there and create a new section for <languageKey index="de" type="array"> for German. Then fill in the translation for each.
I believe there is a tool to help you out with this, and you can read about it at http://typo3.org/extensions/translators/ under Translating Extensions.
Also, you can translate the locallang_db.xml file too which is for the Backend. That way, when records are inserted in the Backend, it can be in German too.
Let us know if you have any more questions, and if I can't help, I am sure there is someone else who can.
-Dave