Don't misunderstand me, I can see your point, and it would be a feature I might want to use in some cases.
But apart from the data and tech you need people implementing it, and I can understand most companies not seeing covering your/our case as worty of the added development/maintenance cost that it would entail.
I've been doing eCommerce for a long time now and the number of site that realize this is shockingly limited.
With a few exceptions, the translations you are using for a country website's language are possible to use for any country where a visitor wants to use the language. Exceptions include things like country specific product features and such. Those kinds of things would need a little though.
The data is all there and the tech is all there. It's just a desire or realization that is missing.