Ubercart and E-Commerce are two separate projects.
Ubercart is turning into "Drupal Commerce", which is not the "E-Commerce module".
I don't think many people use the E-Commerce module (500ish users), so I think Ubercart (20,000ish users) is kinda taking over the namespace.
As for improving the i18n support, I think it's a problem with most modules in Drupal. Find and report bugs. Submit patches. Hope they get integrated.