code: def validate_lang(ctx, param, lang):
      
      if ctx.params['nocheck']:
          return lang
  
      try:
          if lang not in tts_langs():
              raise click.UsageError(
                  "'%s' not in list of supported languages.\n"
                  "Use --all to list languages or "
                  "add --nocheck to disable language check." % lang)
          else:
              # The language is valid.
              # No need to let gTTS re-validate.
              ctx.params['nocheck'] = True
      except RuntimeError as e:
          # Only case where the <nocheck> flag can be False
          # Non-fatal. gTTS will try to re-validate.
          log.debug(str(e), exc_info=True)
  
      return lang
docs: Validation callback for the <lang> option.
      Ensures <lang> is a supported language unless the <nocheck> flag is set