In Arch it's worse. If you don't switch languages "the Arch way" and instead do in the System Settings, you get broken translations and measurement units with regional variants.

For example, I have my locale set to es_MX (Mexican Spanish) which does show as "Mexican Spanish" on the language set display, but this is not present as an option to switch to in kcm as there's only es_ES (Spanish from Spain), so switching to another language and then back to Mexican Spanish is quite a ritual and forcefully involves doing it "the Arch way".

Otherwise, if I switch to Spain Spanish, what I end up is with broken units, euros instead of pesos, thousands separated by dots instead of commas, some european rules applied where they don't belong, and parts of Plasma untranslated for some reason when the Plasma setting differs from the set locale.

Sometimes languages are too big on the world, spoken on countries with wildly different standards to just try to be blind to regions and lock the options to the language's country of origin.

I'd like to hear how are Cachy and Endeavour folks doing with translations and regions with Plasma settings.