public function keys()
    {
        $locales = array_map(function (LocaleCollection $locales) {
            $keys = $locales->keys()->toArray();
            return array_combine($keys, $keys);
        }, $this->locales);

        $all = [];

        foreach ($locales as $keys) {
            $all = array_merge($all, $keys);
        }

        return $all;
    }