Quoting: cubic
I'm thinking of language being a reflection of culture, as you are saying. Then, if the culture changes rapidly, maybe language (which is optimised for the previous culture) will no longer be optimal for reflecting the new culture. I'm not sure that could really happen, I was just speculating!
OK, I think we've been talking about different scopes here. I meant culture and lanuage on a human scale. You seem to be comparing different cultures with different linguistic assets. In that case, sure, I think in some cases a clash like that may become cataclysmic. Some anthropologists maintain that this is what enabled the Cro-Magnon to hold the upper hand over Neanderthal (specifically physiological defficiencies of speech organs in the Neanderthal. The theory recently suffered a little booboo due to a discovery of some fossilized bone fragments, but still it isn't knocked out of circulation).
It's a very fascinating subject to me, and I will gladly continue the chat, giving proper answers to the other parts of your post. Of course that will depend on your continued interest, and on the admins who may decide we have hijacked this thread.