That is only referring to the language of the buttons for add to cart and checkout and other aspects of the eCart system.
creating a multiple language cart is best done by using subdomains:
eng.shop.com
ger.shop.com
and using a separate database table for each shop language version
the admin section can be configured to access both database tables to manage the data.
you can even create the insert pages to insert to both the english table and the german table at the same time.