code: @SuppressWarnings("serial")
      private Component createAddDescriptorButton() {
  
          Button addDescriptorButton = CmsToolBar.createButton(
              FontOpenCms.COPY_LOCALE,
              m_messages.key(Messages.GUI_ADD_DESCRIPTOR_0));
  
          addDescriptorButton.setDisableOnClick(true);
  
          addDescriptorButton.addClickListener(new ClickListener() {
  
              @SuppressWarnings("synthetic-access")
              public void buttonClick(ClickEvent event) {
  
                  Map<Object, Object> filters = getFilters();
                  m_table.clearFilters();
                  if (!m_model.addDescriptor()) {
                      CmsVaadinUtils.showAlert(
                          m_messages.key(Messages.ERR_BUNDLE_DESCRIPTOR_CREATION_FAILED_0),
                          m_messages.key(Messages.ERR_BUNDLE_DESCRIPTOR_CREATION_FAILED_DESCRIPTION_0),
                          null);
                  } else {
                      IndexedContainer newContainer = null;
                      try {
                          newContainer = m_model.getContainerForCurrentLocale();
                          m_table.setContainerDataSource(newContainer);
                          initFieldFactories();
                          initStyleGenerators();
                          setEditMode(EditMode.MASTER);
                          m_table.setColumnCollapsingAllowed(true);
                          adjustVisibleColumns();
                          m_options.updateShownOptions(m_model.hasMasterMode(), m_model.canAddKeys());
                          m_options.setEditMode(m_model.getEditMode());
                      } catch (IOException | CmsException e) {
                          // Can never appear here, since container is created by addDescriptor already.
                          LOG.error(e.getLocalizedMessage(), e);
                      }
                  }
                  setFilters(filters);
              }
          });
          return addDescriptorButton;
      }
docs: Returns a button component. On click, it triggers adding a bundle descriptor.
  @return a button for adding a descriptor to a bundle.