code: static public function getLocaleWithSuffix($separator = '_', $lowercased = false): ?string {
          $locale = preg_split('%[-_]%', strtolower(app()->getLocale()));
          if (count($locale) === 2) {
              return $locale[0] . $separator . ($lowercased ? $locale[1] : strtoupper($locale[1]));
          } else {
              $localeSuffix = isset(static::$localeSuffixMap[$locale[0]]) ? static::$localeSuffixMap[$locale[0]] : $locale[0];
              return $locale[0] . $separator . ($lowercased ? $localeSuffix : strtoupper($localeSuffix));
          }
      }
docs: Get locale in format "en_US" or "ru-RU" or "it-it"
  @param string $separator
  @param bool $lowercased - true: will return "it-it" instead of "it-IT"
  @return string