Fully up-to-date KDE Neon has for some bizarre reason changed the language setting of the OS and any non-specified-language application menus to Norwegian.
I have gone into Language settings and set language to British English (no other language in the list). I have logged out and back in and also restarted the PC. Still in Norwegian.

My location/time-zone is Oslo (correct) but as a Normal Human Being i never asked for this, this Norsk tulle språk. As a developer this is a pet peeve of mine, to change a vital setting without the consent of the user based on location!

Why did this happen and how can I get back to English?

How can I avoid this silliness in the future?


Edit: I have also my Regional Settings > Formats to Brit. English and this too has no effect after log out/log in or a restart.

I can't speak to how to prevent such a thing in the future, but issuing "sudo dpkg-reconfigure locales" in a terminal should get you back on your feet. My best guess is that you want to choose en_GB.UTF-8 UTF-8.

Good news, it is back in English, including the date on the log-in screen.
I fiddled around with it and logged out/in several times.

I hope this never happens again.