UK English translation glitches

Hi,

Something is fishy with the European (UK) English translation on Mac. It does its job the way you'd expect on Linux, but on Mac the only parts that show U English translations (~ise vs. ~ize, ~our vs ~or) are widgets provided by KF5 frameworks, like the KTextEditor bits of the settings dialog.
Curiously, the French translation does work on Mac so whatever the issue it is not with the translation feature itself.

Any ideas?

R.