Changing language

If you set in wp-config.php:

define ('WPLANG', 'de_DE');

the frontend will be in German.
If you want the backend to be translated, install plugin Wppa Admin Language Pack

Note: the translations may not be complete.

Thank you, that workes great, also that link is very helpful:
https://wppa.opajaap.nl/wppa-tutorial/how-to-translate-wppa/

Best regards, Kalle