I've made some little changes to your plugin in order to make translation fully functional. Furthermore, I've added the italian translation.
If you are interested in to merge my updated code in your plugin, you can download it here.
You will found 1 new line of code (calling
load_plugin_textdomain) in surveys.php and some strings to which I've added the
e() function. Ah, and I reverted to "save As" the output of the CSV export function.
Nothing more, nothing less.
Thanks for your work.