Chouby, please, let me congratulate you on this work.
The situation is solved:
WP e-Commerce's add to cart Fancy Notification translated with Polylang
I started checking yesterday what to do about it. As I said before, jQuery is not easy.
Regarding the calendar plugin jQuery you showed me, $.ajaxSetup use is not recommended by the jQuery team:
jQuery.ajaxSetup use not recommended
I was looking for an alternative when I saw your post.
Thank you, Chouby.