Basically we don't want to add stuff to libglade that it is specific for a GUI builder like i18n information or other things like that.
We shouldn't depend on libglade adding this kind of stuff because it is not designed for that. It just ignores this kind of information because applications don't care about it.
Having said that it doesn't mean libglade should not accept some other changes to accept new GTK+ features. IMHO libglade is starting to show its age (7 years) and it's been a while since it has not added a GTK+ feature.