`Plurals` doesn't work for some locales

Problem

The Plurals component only outputs a plurals.rb file for a locale if the locale appears exactly in the supplemental/plurals.xml file.

For example, zh-Hant doesn't have a plurals.rb file, which means that it would fall back to its parent locale, root. root happens to have the same plural rules as zh-Hant (i.e., everything uses other) so it isn't an issue.

However, there are locales that fall back to root that don't share the same plural rules as root. For example, sd-Deva falls back to root, but (as I understand it) sd-Deva uses both one and other. So if it were to use root's plurals.rb, it would be incorrect.

Potential Solution?

IDK yet.

Start by locating the Plurals component and tracing how it uses supplemental/plurals.xml to decide which locales receive a plurals.rb file. Compare the generated handling of zh-Hant and sd-Deva with their CLDR locale fallback rules. Done means locales falling back to root receive plural rules appropriate to the locale rather than blindly inheriting root's rules.