I think a UI tweak is needed so that the user doesn't have to select which language he wants to translate to (since it's usually the same one), after he/she already selected the language.
This should be remembered throughout page loads via a cookie or something similar.
Of course, there should still be a way for the user to switch back to another language, so the UI should account for that, but my main point is that the Translate button should just be a 1-click once it knows the language the user wants.
Thoughts?
P.S. Thank you for creating this plugin. It's getting close to perfect :)
http://wordpress.org/extend/plugins/google-ajax-translation/