Hi, Got some strange bug. Removed cart from usermenu, added new 'winkelwagen' to main menu (all dutch) when adding products I see 'cart' in url??? Looks like 2 carts are present? Going nuts.... url:ook-leuk.nl
I can still see "cart" in top menu. So change it and make sure there is no other menu items like that in other menus or trash. Check redirections component as well and SEF component if You are using other than default joomla one.
Don't know why but I solved it finally by deleting 'cart' and create a new 'cart' and rename this. I'm not using any sef plugins. My guess; language was set after install and 'locked' for vm cart.