Parsing system locales

[Finchiedev]

Hello all!

I've been experimenting with integrating icu4x into user-facing applications for a while now, and was very excited to see the progress made by GSoC student @ashu26jha in #5081 and #5358 on retrieving the system locale. If there is interest in doing so, I would be very interested in contributing to the env_preferences crate that came out of this work to make it easier to use out-of-the-box.

This is motivated by my computer (x86_64-unknown-linux-gnu) returning Ok({All: "C"}) from the linux implementation of env_preferences::get_locales. Ideally, env_preferences::get_locales would return Locale instead of String, so I can immediately use the unwrapped result with icu_datetime, icu_plurals etc. I assume parsing these strings into locales is the kind of logic that should be handled by icu4x rather than duplicated across downstream users - but please correct me if I'm wrong!

At least on Linux, I would expect to solve this according to TR35's section on legacy variants. If possible, I'd love feedback on this solution, and if there's interest in such a contribution at all. I am very happy to do the work but don't want to interfere with anyone's existing progress or create an unwanted PR :)

[Manishearth]

Yes, we'd welcome contributions!

I think the legacy variant section is correct, though note that ICU4X doesn't ship any data around these by default.

@sffc to confirm that this is the route we should take.