docs: function onFinish(output) {
      var book = output.getBook();
      var outputRoot = output.getRoot();
  
      if (!book.isMultilingual()) {
          return Promise(output);
      }
  
      // Get main language
      var languages = book.getLanguages();
      var mainLanguage = languages.getDefaultLanguage();
  
      // Read the main JSON
      return fs.readFile(path.resolve(outputRoot, mainLanguage.getID(), 'README.json'), 'utf8')
  
      // Extend the JSON
      .then(function(content) {
          var json = JSON.parse(content);
  
          json.languages = JSONUtils.encodeLanguages(languages);
  
          return json;
      })
  
      .then(function(json) {
          return fs.writeFile(
              path.resolve(outputRoot, 'README.json'),
              JSON.stringify(json, null, 4)
          );
      })
  
      .thenResolve(output);
  }