Assuming you're on the right trail (considered it myself as well), then the location would be or varrack castle or the mysterious old man, as they both have readable books. (Ideally we should check out the names of various locations both in english, french and german and compare them with their respective clues) I already tried MoM One would actually need to try out all the different book shelves in his home... but I think it will be far more complicated. E.g. that they made some random bookshelve in some random home readable and that the clue points us to that exact home or something like that :/ Hmm...