Custom function inside menu defined in ui file

Development
1

I’m trying to use different translation system than gnome is used to. Problem arose when I’ve tried to use it inside Ui files. I’ve created custom utility function translate :: str → str, but it seem not to work inside menus:

<object class="GtkMenuButton">
  <property name="menu_model">
    <menu>
      <section>
        <item>
          <attribute name="label">
            <closure function="translate">
               some name
            </closure>
          </attribute>
        </item>
      </section>
     </menu>
  </property>
</object>

this prints

Gtk-CRITICAL **: 13:30:49.720: Error building template class 'MyGtkAppWindow' for an instance of type 'MyGtkAppWindow': Element <closure> not allowed inside <attribute>

and I have no other ideas. How do I do it?