This task description has been updated by aheinecke.
The GnuPG System and GpgOL / GpgEX detect the language through GetThreadLocale or Environment variables on Windows (libgpg-error is responsible for that). This might not be the configured display language and it might also differ from Kleopatra which has a dedicated setting.
A good fix could be that Kleopatra would write a registry Key that notes "it's" Language and that libgpg-error "my_nl_locale_name" would read / respect that language. This would also make it easier for admins to globally configure languages.
Original report was: "Wrong Display Language":
GPGOL shows the wrong display language. My OS and Office is English and the GPGOL is always german.