Lang de_DE updated + not translated error fix

Translation de_DE updated due to latest changes.
Fixed not translated error messages in 'lib/class/error.class.php'
updated mo's & po's.

And could you take an eye on the following? I think it should be more dynamically for other langs. :smiley: 
![styleproblem](https://cloud.githubusercontent.com/assets/6222200/3009595/b993b650-df00-11e3-9479-a2c9b1f58f43.jpg)