Update de_DE.ini

Small factual corrections (encrypt save instead of decrypt save) and consistency errors (audio settings was translated inconsistently).
Grammatical and formal improvements.
Layout/ordering adjusted to match the enUS.ini template. Looks messy now, will be great later.

Some entries were missing compared to enUS (Up in [General]; Select, Start in [Dialog]), added these with tentative translations, I'm not sure where these actually show up. I can't translate Shift without context either so it will stay for now.