Oh, that's a hard one. It really depends on what you want to learn. While I can recommend each and every of the smaller Teubner books, they can be quite pricey since the new edition is not as good as the older ones (on the upper shelve). However, the big Teubner "Deutsche Küche" and "Küchenpraxis (lowest shelve) are wonderful too, and you can get them relatively inexpensive on eBay. If I had to choose just one, I'd go with "Küchenpraxis" since it's the most comprehensive for Wares, Produce, Procedures and an assortment of recipes.
Note that that's a recipe book. No pictures, no hand-holding, no nothing, but lots and lots of starting points. If you've ever asked yourself a question ranging from "How to make a proper Bechamel" to "What in the everloving fuck am I supposed to do with quail eggs", Escoffier has you covered. As to German stuff the founding bible of modern German cooking is "Was Männern so gut schmeckt". The title is from a different age which is a shame means it's not in print any more and used paperbacks easily go for 20 bucks. Library might have it, also, your parents.
Thanks! yes, all recipe books. The old ones are two German late 19th and early 20th century books and the one on the far right is a British cook-/household book from 1807.