use Intl.Locale for langneg

[ImUrX]

Requires fixing some test errors

[eemeli]

The test errors seem rather significant here, as they're changing the behaviour of the locale matching. Given the different treatment of subtags like macos and ca-japanese in our locale.ts and the standard Intl.Locale, I'm not sure that these are easily reconcilable without some observable changes.

Effectively, this is pointing out that our current understanding of locale tags is nonstandard, and that's a bit of a problem.

I wonder if we could use Intl.Locale for matching on language, region & script, and do something else for the rest?

[ImUrX]

Yes as you can see I handle the private-usage part by just reading the last subtag (because its always the last one), what should I do?

[ImUrX]

I also personally ended up using a ponyfill of the Intl.LocaleMatcher standard proposal in my code.

[eemeli]

Yes as you can see I handle the private-usage part by just reading the last subtag (because its always the last one), what should I do?

I see that. Hmmm. Could you make use of the normalization done in the baseName? As in, split it by - and compare the parts for each locale? That might allow for the implementation change to be considered a relaxation of the variant regexp.

[eemeli]

Closing in favour of #605.