Unfortunately there is not much information for this online (atleast from a quick search I didn’t find much)
Most seems to be related to working together with publishing houses (I loathe the German publishing houses so that’s definitely no option).
I would prefer working directly with an independent author - when I have a bit more time I’ll check out how to best get in contact with them.
Not sure about the legal side of it, but I have a friend who works in German copyright and who could probably help figure that part out.
They are author as opposed to translator-focused, but maybe reaching out to them can be a first step in getting the lay of the land? They might have some information about how their authors tend to use translation services. Although I'm sure there must be some translator communities out there that could provide even more focused info.
I would prefer working directly with an independent author - when I have a bit more time I’ll check out how to best get in contact with them.
Not sure about the legal side of it, but I have a friend who works in German copyright and who could probably help figure that part out.