code: private function strippedUri(Request $request): ?string
      {
          // Strip leading slash.
          if (null === $request || '' === $requestUri = rawurldecode(substr($request->getPathInfo(), 1))) {
              return null;
          }
          if ($this->isLocalePrepended) {
              $matches = [];
              // Use the matches instead of substr() (thanks to Mario Müller)
              if (preg_match('@^([a-z]{2}(-[A-Z]{2})?)/(.*)$@', $requestUri, $matches)) {
                  $requestUri = $matches[3];
              }
          }
  
          // Remove the URL suffix if not just a language root (e.g. en/) is requested
          if ('' !== $this->urlSuffix && '' !== $requestUri && (
                  !$this->isLocalePrepended || !preg_match('@^[a-z]{2}(-[A-Z]{2})?/$@', $requestUri)
              )) {
              $requestUri = substr($requestUri, 0, -\strlen($this->urlSuffix));
          }
  
          return $requestUri;
      }
docs: Strip the leading locale (if any).
  
  @param Request $request The request.
  
  @return string