docs: def default_language_from_metadata_and_ext(metadata, ext):
      """Return the default language given the notebook metadata, and a file extension"""
      default_from_ext = _SCRIPT_EXTENSIONS.get(ext, {}).get('language', 'python')
  
      language = (metadata.get('jupytext', {}).get('main_language')
                  or metadata.get('kernelspec', {}).get('language')
                  or default_from_ext)
  
      if language.startswith('C++'):
          language = 'c++'
  
      return language