public function addMultiLanguage(...$parameters)
    {
        if (count($parameters) === 1) {
            $this->routes['ml'][] = ['closure' => $parameters[0], 'groupArgs' => []];
        } elseif (count($parameters) === 2) {
            $this->routes['ml'][] = ['closure' => $parameters[1], 'groupArgs' => $parameters[0]];
        } else {
            throw new \InvalidArgumentException;
        }
    }