improved German translation (2nd attempt)

[rbergmair]

I took a second stab here at #327, this time without binaries.

Just to repeat the info:

I'm a German native speaker, and I took a stab at improving the German translation tokens.

• added translations for some tokens that previously didn't have any translations at all
• fixed some translations that I found highly unidiomatic. (For example "Vorlieben" for "Preferences" sounds pretty weird to my ear).
• fixed some inconsistencies in spelling conventions e.g. upper-casing of personal pronouns (e.g. "Du" and "Dich" was previously upper-cased in line with conventions for writing letters in some, but not all cases. I uniformly used the lower-case version instead).