>>5 Good news: I finally found the original german dub for Mystery of the Third Planet! It was posted rather recently at the beginning of april on Youtube... Found it only by chance, when I was curious and tried finding german dubs of soviet cartoons, since germany was once famously occupied by the soviets for a long time and DEFA, the studio, which was founded in the soviet occupation zone in germany and therefore responsible for distributing many soviet films there. Also being able to speak not only russian, but also german, like I do, helped a bit :).
Here's the link to the dub: link
The dub is pretty well done, competently made and not bad at all, voice actors are also doing a good job, though I would still rather watch this film in it's original language, simply by habit alone :).
Nevertheless it's a very cool curiosity for sure and though a few the attempts at translating the russian into german are clunky, it still has some charme to it and at least it is in my opinion better made than the german dub for ''The Little Humpbacked Horse''(1975). Also it's still bizarre to me seing something you grew up watching in your native language, only to discover it has a dub made for it in a foreign language you know, but only recently found out about it..
I will try and find other german dubs of other animated films on here and post the links to them in the comments under the respective films, simply out of curiosity and for the others, who might want to find out, how the films were translated into german and which changes they made to the dialogue, which I must imagine must be a real pain in the butt, because of the difficulty during the translation (since russian and german are very incompatible), though I'm sure that's not a new problem in dubbing.