How to comprehensively change my locale choice after installing antiX?

I've installed antiX Linux (v19.3), with a certain locale (let's say it's xx_XX.UTF-8). After installation, I've had a change of heart and want the locale for all users to be/to default to something else (yy_YY.UTF-8). How do I make that change _comprehensively_ (i.e. leaving no user, app or configuration file believing the locale is or used to be xx_XX.UTF-8)? Note: Answers about Debian-based distributions in general are also ok.