I think GUI libraries which offer C bindings are easy to wrap in other languages, that is why I like Gtk a lot. In my eyes, it works especially nice with Go. Tk should be easy to wrap for Go to, but usually one would prefer Gtk, when there is a choice :).
GUI libraries often rely on specific language features so they are hard to wrap in other languages. That's why good GUI libraries don't exist in ANY language other than the ones they were written in.