German is not available yet in version 580, because the change below has not been done yet.
Please contact the translator to update his translation.
You must change the German.lng file anyhow as follows:
ProgDef = jv16/PTLite
instead of
ProgDef = jv16/RSPro/RS
If you do not change that, it will not work!
You can make the change yourself with Notepad...
Just open the German.lng file in the directory Languages and do the change as mentioned above.
Note: In MS Vista, when PowerTools is installed in the default directory (i.e. C:\Program Files\jv16 PowerTools 2009), maybe you'll have to "take Ownership" of the German.lng file before you will be able to change it.