Remove inconsistencies and mistakes in German translation

[Marc Nause]

The German translation of the app contains

• mistakes (e.g. "Aktie" <-> "share", should be "teilen", typical Google translate mistake)
• inconsistencies (e.g. mixed usage of Duzen and Siezen, using both "Fähigkeiten" and "Fertigkeiten" for "skill")

The mistakes in the translation should be corrected and inconsistencies should be removed.

I am willing to work on the German translation.

[Gunjan Paul]

i will love to work on this issue, so may you tell me which is the exact file?

[Retoc]

See my Pull Request #2386 which contains many of the requested changes and improvements and is a big step forward.