I've driven all over the planet except for Asia and Africa. So far, no real problem and I think most drivers would adapt within a day or two. Greece, Panama and Colombia stand out as somewhat more exciting. Switching to left hand driving in the UK also wasn't a big problem but you do have to pay more attention.

Of course I may have simply been lucky, but given that my driving license is valid in many countries it seems as though humanity has determined this is mostly a solved problem. When someone says "Put a Waymo on random road in the world, can it drive it?" they mean: I would expect a human to be able to drive on a random road in the world. And they likely could. Can a Waymo do the same?

I don't know the answer to that one. But if there is one thing that humans are pretty good at it is adaptation to circumstances previously unseen. I am not sure if a Waymo could do the same but it would be a very interesting experiment to find out.

American suburban streets are not representative of driving in most parts of the world. I don't think the bar of 'should be able to drive most places where humans can drive' is all that high and even your average American would adapt pretty quickly to driving in different places. Source: I know plenty of Americans and have seen them drive in lots of countries. Usually it works quite well, though, admittedly, seeing them in Germany was kind of funny.

"Am I hallucinating or did we just get passed by an old lady? And we're doing 85 Mph?"