code: @UiHandler("m_localeSelection")
      protected void onLocaleChange(ValueChangeEvent<String> event) {
  
          String value = event.getValue();
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(value) || value.equals(NOT_SET_OPTION_VALUE)) {
              value = m_currentLocale;
          }
          m_tabHandler.setLocale(value);
      }
docs: Handles the change event of the locale select box.<p>
  
  @param event the change event