I suggest Montague Summers, History of Withcraft and Demonology, which was written right in the time range you're looking for, and while British rather that German, looks worldwide and was written by someone who is in that space between Catholic and Protest. Also it's public domain and available for download/reading on Archive.org. I suggest chapter 6, Diabolic Possession, starting here : https://archive.org/details/in.ernet.dli.2015.173667/page/n223/mode/2up It'll give you a good broad overview of what was known/believed at the time without the modern paganism/catholicism overlay you'll see on most newer stuff even if it's trying to be historically based.