Basically, #musl's locale support has been pretty abysmal for a long time.
This is in contrast to multilingualization, which has always been first-class. M17N basically means ability to represent data in your own and other languages concurrently, and is about character set and avoiding artificial limitations. Locale/localization, OTOH, means the ability of the software to adjust its behavior and presentation to the norms of a particular cultural context, and that's what we've failed at.
About 10 years ago, I wrote the initial locale implementation, but it never received testing/feedback, and had core data representation bugs that basically made it not usable.
5/N