Well, I imagine the EN localization team doesn't actually talk like that IRL, so they keep using the few words they know without making the dialog overcomplicated (like Urianger).

Like, if you had to choose between having Urianger-tier dialog in every quest or these repeated "ye olde" words in text, I'm sure most would prefer the latter.

(and no, plain English is not an option at least for the eorzean side, maybe for other continents)