Hi,
You have two translations
VENDOR_CART_PRODUCT_REFUSED="Can't add product "%s" of vendor %s"
VENDOR_CART_PRODUCT_REFUSED_2="Can't add product "%s" of vendor %s"
These translations are used when you have a vendor limitation.
The second one is used when the customer is trying to add a product and have already products from one vendor (and from the store too).
It received 4 strings : the product name, the vendor name of the refused product, the current vendor name in the cart, the vendor name of your main vendor.
The first one is used when the customer is trying to add a product from another vendor.
It received 3 strings : the product name, the vendor name of the refused product, the current vendor name in the cart.
You can override these translations in order to have special custom messages to warn the user.
Regards,