Sorry, one small point. There's no such language as Australian Aborigine. Rather, there are (currently) around 100-150 seperate languages that are classed as 'Aboriginal languages'. They're regional, but they're not all dialects, and knowing one is no guarantee that you'd understand another. Someone who can speak Tiwi probably wouldn't understand Ngaro, for instance.

I wonder if something similar holds true for Native American languages?

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