Message:setLanguage() and Message::getLanguage() operate on the wrong property

I think it is intentional. I think it is done this way so the message can be toggled te different languages.

/**
   * Set the language that should be used.
   *
   * @param string $language
   *   The language to load from the message template when fetching the text.
   */
  public function setLanguage($language);