yii\helpers\BaseInflector::pluralize PHP Method

    public static function pluralize($word)
    {
        if (isset(static::$specials[$word])) {
            return static::$specials[$word];
        }
        foreach (static::$plurals as $rule => $replacement) {
            if (preg_match($rule, $word)) {
                return preg_replace($rule, $replacement, $word);
            }
        }
        return $word;
    }