if (!isset(self::$_singular['cacheUninflected']) || !isset(self::$_singular['cacheIrregular'])) {
            self::$_singular['cacheUninflected'] = '(?:' . implode('|', self::$_singular['merged']['uninflected']) . ')';
            self::$_singular['cacheIrregular'] = '(?:' . implode('|', array_keys(self::$_singular['merged']['irregular'])) . ')';
        }