Though i18n-js does let you write your own pluralizations rules (taken from the readme), while supporting zero/one/many out of the box:

    I18n.pluralization["ru"] = function (count) {
      var key = count % 10 == 1 && count % 100 != 11 ? "one" : [2, 3, 4].indexOf(count % 10) >= 0 && [12, 13, 14].indexOf(count % 100) < 0 ? "few" : count % 10 == 0 || [5, 6, 7, 8, 9].indexOf(count % 10) >= 0 || [11, 12, 13, 14].indexOf(count % 100) >= 0 ? "many" : "other";
      return [key];
    };