Try to load glade-file and define a translation domain as the last parameter,
but you don't specify a root-widget (second parameter). See this snipped below:

use Gtk2 -init;
use Gtk2::GladeXML;

our $gladexml =
Gtk2::GladeXML->new('myuserinterface.glade',undef,"myuserinterface");

This throws an error:
(userinterface.pl:25060): libglade-CRITICAL **: file glade-xml.c: line 1198
(glade_xml_build_interface): assertion `wid != NULL' failed

The above snipped should be fine, it should be possible to specify a translation
domain without defining a root element. If I use this:

our $gladexml =
Gtk2::GladeXML->new('myuserinterface.glade','mainWindow","myuserinterface");

everything works fine.
I found also a ruby-example, which uses my syntax:

@glade = GladeXML.new('myapp.glade', nil, 'myapp') ...