private static function localeFormat($part = 'datetime')
    {
        if (self::$localeFormat === null) {
            $locale = self::getLocale();
            $file = resource_path('lang/' . $locale . '/datetime.php');
            if (file_exists($file)) {
                /** @noinspection PhpIncludeInspection */
                self::$localeFormat = include $file;
            }
            else {
                $file = resource_path('lang/' . config('locale.fallback') . '/datetime.php');
                /** @noinspection PhpIncludeInspection */
                self::$localeFormat = file_exists($file) ? include $file : ['datetime' => 'Y-m-d H:i', 'date' => 'Y-m-d', 'time' => 'H:i'];
            }
        }

        return self::$localeFormat[$part];
    }