I think this is one of those things that like 0.1% of even British people would ever notice or care about I'm afraid ;-).

A bit like trying to replace "ass" with "arse", a futile exercise.

I wouldn't be wholly against the idea except we have literally cart pictures in our iconography, so it would require some work.

To answer your question...

The American English option does change a lot of spelling over to American. E.g. "Catalogue" becomes "Catalog" and "Colour" becomes "Color".

It may give you a little happiness back if I tell you the underlying name for the config option (i.e. in the code) is slightly sarcastic: "yeehaw".

Haha, yes that put a smile on my face :) I was reading an article on some webmaster forum about the cart/basket terminology and the consensus was that basket was the de facto for UK websites, cart is American all the way. It also said that most UK sites use the term basket but use an icon of a cart/trolley so I wasn't intending to change the icon/pictures. I just think Basket is a better fit (along with everyone involved in that discussion). I can change that myself though :)