Books in other languages
Der Westfälische Frieden by Fritz Dickmann
If you do read German, this book is still the standard. Dickmann is more interested in the negotiations as a phenomenon in the internal history of the Empire, but he does not ignore international events by any means.
Bibliographie zum Westfälischen Frieden, edited by Heinz Duchhardt
If you want to find out about more sources on the Peace of Westphalia, this massive bibliography contains an incredible list, and it is only about 15 years old. Unfortunately, the last 15 years have seen a further outpouring of works on the Peace of Westphalia, and there is no comprehensive place to find them.