private function fetchLocales($available = true)
    {
        $available_locales = $this->getAvailableLocales();
        $current_locales = $this->translations()->lists('locale')->toArray();

        return array_filter($available_locales, function ($v) use ($current_locales, $available) {
            return $available ? in_array($v, $current_locales) : !in_array($v, $current_locales);
        }, ARRAY_FILTER_USE_BOTH);
    }