I don't know either, I just copied that code from the widget.rpc module.  The template code in set-original-language.html (and I think other places) uses this piece of code to display the language:

video.subtitle_language.get_language_code_display.  If the subtitle language doesn't exist, then this doesn't work.

Seems like we could add a video.get_language_code_display() method that would use the audio language that's stored in the Video object.  If you think that's a good idea, I can try to code that up.