Hello,
From backend of your website I see that you have change ADD TO CART via Language Manage. This only for single product.
But we I can not see 2 others constants for ADD TO CART in your website - COM_VIRTUEMART_CART_ADD_TO.
But They present in default theme.
See attached image
So, please remember what you did last and return default settings.
Sincerely Yours
Taras
OrdaSoft team