Thanks Jim!
Yes, changing the display language from English (United States) to German (Germany)/Deutsch (Deutschland) works. However, then Windows is of course completely German, which is not exactly what I would've liked.
I didn't test it yesterday, as I'm behind a WSUS, so language packs aren't (easily) available. However, I managed to get two to test, English (Germany) and German (Germany). The one that changes the location to Germany, but keeps everything in English is not enough.
Interestingly, JRiver can be kept completely in English. It feels like it is passing this setting through or something. It would be cool if it had like an override/ignore setting, so I don't have to switch Windows to a different language (which also requires me to sign off and on again).
Something like Tools-->Options-->Video: "Disc Menu Language:" Options: "Windows default" and "select language from list"
Could something like this be relatively easy to implement?