[aphexairlines]

How do you use WPF from java or cpython? How do you use the webOS ui from haskell? How do you use the Android UI from ocaml?

Open source core libraries are written against the C ABI (even when employing object models like GObject) so that everyone can bind to them easily. For example:

http://www.gtk.org/language-bindings.html

http://cairographics.org/bindings/

http://www.freedesktop.org/wiki/Software/DBusBindings