I have similarly basic needs, and I stopped distro-hopping when I found Q4OS a few years ago. It seems to run well on most hardware and, while I can’t speak as to how well-supported it is in German, its community is based in Germany.

If you want to recapture the feel of early D&D, ShadowDark (quickstart book) looks like it’s going to be pretty good. The simple tweaks to the current game make a big difference, and the artwork is spot-on. This is the image grabbed my attention when I fist saw it (and realized it was new).

Dave Trampier is the most obvious influence, but the art also reminds me of Garry Chalk’s illustrations for Joe Dever’s Lone Wolf books and the early editions of Talisman. Now that I mention them, Lone Wolf game books and the original Talisman board games are worth familiarizing yourself with if you really want to get into the old-school experience…