Changing policies in packaging Windows Installer
There are gtk20.mo, glib20.mo etc. translations (under /bin/) of all languages from GTK+.
Software which translation is incomplete is worse than software that is not translated at all. It also make a severely bad impression for RTL users (i.e. seeing a Latin UI from Right-to-left).
If gajim.mo is not available in locale X then do not include X locale it in the installer.