Just to give a quick +1 to the things kulvik says. I think he's had the most success doing multilingual w/ Ubercart, but he's also got the coders on hand to adjust the modules to make it work. A goal for the next version of Ubercart is to remove all the form customizable strings (like button titles, field titles, etc.). This is the main thing breaking multilingual support. We put them in there to make the cart easily modifiable in those places, but we weren't familiar with all the issues related to multilingual Drupal sites at the time.

In the future, after this change happens, we'll refer folks to the translation modules when they want to rename various parts of Ubercart.