I've ranted bitterly over the years about the limitations of date and time formatting in KDE 5, after the flexibility we had in KDE 4. Today I Learned a couple of points about this:
Also, the systems setting screen for this doesn't work in my KDE 5.27.4; I click on choices and it exits without changing most of the time. I suspect the new (apparently) Kirigami based "kcm" is buggy.
- The fault (to put it mildly, I'd start with asinineness) lies with the POSIX standard. It's in that that the assumption that everyone in a country uses the same date and time formats (with the choice of a long and short form). Qt and KDE just want to to be standards compliant. The standard itself is arguably wrong in many countries, including mine. I suspect that standards folks instinctively want to standardize.
- Many users in the English speaking world need to use 24 hour clock times, and resort to using English - Denmark, en_DK, to get them. I've just found that English - Sweden is even better, because it also gives you ISO 8601 dates! (Someone should lecture the POSIX people about ISO standards.) Unfortunately my 23.04 English install does not have the en_SE locale, but some random post pointed me to this github gist that set up the en_SE locale.
(It didn't work at first because somehow LC_ALL was being set somewhere. That should not ever be set globally as it overrides all the other settings, but I failed to track down the setting; it wasn't anywhere in my $HOME nor anywhere in /etc. So now I nuke it all over the place, to allow the LC_TIME=en_SE.UTF-8 to work.)
Also, the systems setting screen for this doesn't work in my KDE 5.27.4; I click on choices and it exits without changing most of the time. I suspect the new (apparently) Kirigami based "kcm" is buggy.