Improve German localization [Part 3]

[H0mebrewL0ver]

As discussed in https://github.com/V10lator/NUSspli/pull/331#issuecomment-2243396848 I split the improvements into multiple PRs. Part 3 contains:

• rewording of some messages that still need to be discussed

I don't like the translation of is DLC/Update/Demo. This looks really weird

MARIO KART 8 ist DLC.

I think something like the following would be much better

MARIO KART 8 Art/Kategorie: DLC

I hope I've got everything in these three parts, otherwise this PR would be the best place to add all the missing stuff. Furthermore, I hope this is what you meant with

You do that by creating new branches, then doing just some of the work in each branch, then doing PRs for each new branch you created