Hi,
First of all thanks for this great plugin Qian!
I made my "dirty hack" to remove the ugly <!--:en-->...<!--:-->... texts on the nav menu admin page:
It's mostly a javascript based solution and it's not perfect, but it does these things:
- adds a language meta box, so user can choose a qTranslate language
- replaces the most important dirty (<!--:en-->...<!--:-->) texts, labels, and input values with the actual language part
- updates the "hidden" dirty language part when the user change the navigation label's value
- restore the updated ugly values of navigation labels when user save the menu or refresh the page
Attachments:
rename it to functions.php or insert its content into your functions.php - it adds the language metabox and the js file
rename it to qt-nav-menu.js and copy to your theme folder - it makes all the magic

Cheers!