German translation

I'm not sure about some strings:
"bad checksum" would be "schlechte Prüfsumme" but noone says something like that; in it departments something like this would be used in english but you could say something like "Prüfsummen Abgleich fehlgeschlagen"
i don't know any good translation to "bad nospam value" which users would unterstand
i don't know where "call invited" is usesd but i added a translation
Merge pull request #232 from nachfuellbar/patch-1

German translation