code: protected function fallbackFormat($pattern, $args, $locale)
      {
          if (($tokens = self::tokenizePattern($pattern)) === false) {
              $this->_errorCode = -1;
              $this->_errorMessage = 'Message pattern is invalid.';
  
              return false;
          }
          foreach ($tokens as $i => $token) {
              if (is_array($token)) {
                  if (($tokens[$i] = $this->parseToken($token, $args, $locale)) === false) {
                      $this->_errorCode = -1;
                      $this->_errorMessage = 'Message pattern is invalid.';
  
                      return false;
                  }
              }
          }
  
          return implode('', $tokens);
      }
docs: Fallback implementation for MessageFormatter::formatMessage.
  @param string $pattern The pattern string to insert things into.
  @param array $args The array of values to insert into the format string
  @param string $locale The locale to use for formatting locale-dependent parts
  @return false|string The formatted pattern string or `false` if an error occurred