i18n.options.js

export default defineI18nConfig(() => ({
    fallbackLocale: 'en',

    pluralRules: {
        "ru": ruPlurals,
    },
}));

const ruPlurals = (choice, choicesLength, orgRule) => {
    if (choice === 0) {
        return 0
    }

    const teen = choice > 10 && choice < 20
    const endsWithOne = choice % 10 === 1
    if (!teen && endsWithOne) {
        return 1
    }
    if (!teen && choice % 10 >= 2 && choice % 10 <= 4) {
        return 2
    }

    return choicesLength < 4 ? 2 : 3
}