I also have the WP Menu Cart installed. There it says: Choose the menus where you want to display the shopping cart.
I have the free version, so there is only selected the main menu in default language. If I was to add another menu (in the language i want to display) it requires Menu Cart Pro.
Could this be the issue? If so, then why was I able to successfully create two shop -pages, that are similar to each other, but only different languages?