Need to properly deal with plural rules in `i18n.t()`

Looks like [Intl.PluralRules()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/PluralRules/PluralRules) might help, or migrating to a proper I18N framework. I didn't find a lightweight one, but maybe by the pure nature they need to be heavy?