code: def _find_feed_language(self):
          
          self.feed_language = (
              read_first_available_value(
                  os.path.join(self.src_dir, 'feed_info.txt'), 'feed_lang') or
              read_first_available_value(
                  os.path.join(self.src_dir, 'agency.txt'), 'agency_lang'))
          if not self.feed_language:
              raise Exception(
                  'Cannot find feed language in feed_info.txt and agency.txt')
          print('\tfeed language: %s' % self.feed_language)
docs: Find feed language based specified feed_info.txt or agency.txt.