first commit

resources/frontend/core/i18n/pluralizationRules.js

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+module.exports = {
+    /**
+     * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
+     * @param choicesLength {number} an overall amount of available choices
+     * @returns a final choice index to select plural word by
+     */
+    ru: function (choice, choicesLength) {
+        // this === VueI18n instance, so the locale property also exists here
+
+        if (choice === 0) {
+            return 0;
+        }
+
+        const teen = choice > 10 && choice < 20;
+        const endsWithOne = choice % 10 === 1;
+
+        if (choicesLength < 4) {
+            return !teen && endsWithOne ? 1 : 2;
+        }
+        if (!teen && endsWithOne) {
+            return 1;
+        }
+        if (!teen && choice % 10 >= 2 && choice % 10 <= 4) {
+            return 2;
+        }
+
+        return choicesLength < 4 ? 2 : 3;
+    },
+};