This means there is an error in your German language file. More then likely there is something that isn't escaped. Please review your German language files and ensure all ' or " are escaped as necessary examples as follows.
Right:
[code:1]
define( '_UE_TEST', 'Test\'s' );
[/code:1]
Wrong:
[code:1]
define( '_UE_TEST', 'Test's' );
[/code:1]
Notice the string is surrounded by ', but has a ' inside the string. This will cause a fatal PHP error resulting in problems you're experiencing. This same situation can apply to usage of " instead of ;.