> It’s not just about producing the perfect display, it’s about producing the perfect display in response to user input.

Again, what does that have to do with locales and stuff like date/time presentation?

Wayland doesn't give two hoots about languages or fonts or text rendering or time formats; interpreting and displaying that (in repsonse to user input) is up to the application (and/or the frameworks said applications use) to render their output. Wayland is only concerned with getting the application's rendered pixmap to the display (and accurately representing the display capabilities)

Yes, input is the other side of the same coin, but like output, Wayland's input path is a mostly dumb relay of input events from a specific set of input hardware [*] to a specific application. Interpreting those events is up to the application (and/or frameworks).

[*] There's no inherent reason why it has to be "hardware", it's just a stream of logical events. Higher-level input methods (CJK, OSKs, etc) that inject said events into applications have been deployed for a long time now.