I almost mentioned sign language in response to your other post; now that you've brought it up yourself I have to.
I was struck by your comment about language changing how you think about things, because it reminded me of a book on sign language and deaf culture
) in which I'm pretty sure he said that one of the key reasons it was important to teach the deaf to sign was that without true access to a language it is much harder to think; you just don't have all the tools for it.
It was a pretty interesting book overall, though as I recall a bit dry at times. It was quite a while ago that I read it though.