I asked if this was possible and it was marked not planned, so I decided to give it a shot at writing it myself.
I added an extra option to tell the GUI to use my preferred language as both the subtitle and the audio track, I also added a check box to tell the GUI to used the Closed Caption track if it doesn't find a sub that matches the preferred language. I also fixed a few tool tips while I was making the changes.
I added these because I rip a lot of television series DVDs and wanted to be able to always pick the English sub and dub. http://handbrake.fr/pastebin/pastebin.php?show=1564