Extraneous plural variants are generated, causing waste #6
Description
Many locales do not support all plural variants, and some other locales support more than what English and other Latin language has.
For example, Cube shouldn't copy one variants from en-US to zh-Hans as the latter doesn't support the one variant. Xcode does exactly this by hiding unsupported variants for that locale.
Conversely, if there's a new plural variant in the target locale that the base locale doesn't have, Cube should suggest the user to add the missing variants, or add them automatically.
Related, sometimes keys with plural variants will show NEW status despite being fully localized. See screenshot below:
