Thanks. I am already doing something like that, but will go over my settings to see if I'm going wrong somewhere.
Note though that things mostly work. There are just a few (KF5) applications that refuse to play ball (notably KDevelop5 and KWin5, though I notice Kwin4 also uses en_US throughout). I don't expect that's due to an oversight in my tweaking given that those applications also don't behave as they should when I start them with specific settings of the LANG and LANGUAGE variables. R.
