What programming languages should I learn if I am interested in user interface design?

You need to be more specific. Are you interested in Mac, Windows, Linux, or Web based stuff?

Check out Revolution, from http://www.runrev.com – you can learn it really quite easily, as the syntax is very close to plain english, there’s a 30 day trial and in the upper versions you can deploy your app on windows, mac and linux with very little effort.

*Disclaimer – I’m their current graphic designer, but I believe this answer to be beneficial to the user who posted it.

And I should add, Never let programmers near the UI. Trust me and the guy from Panic. I used to live next to the Panic guys. Super awesome.

Panic are incredible, and if you need a great example of UI work check any of their Apps out.

@john: Mac and Web based stuff