I usually prefer English for anything related to development, software engineering, and computers in general. I also run my user interface in English, as it is much easier to search for error messages that way. However, when visiting websites of local places such as restaurants, I prefer the German version and not the one in English meant for tourists.

While third-party extensions allow to switch Accept-Language, it is not in the standard UI of modern browsers. For people like me, an advanced setting of Accept-Language per top-level domain would reduce the number of times I have to find the language switcher on the web page to a minimum.