[ghaff]

From my limited knowledge, companies do tend to handle the tax work for expats. In fact years ago when I was interviewing for an international position where I'd have been moving around a lot, as I recall, they told us something like they'd take some fixed percentage off our paychecks and handle the whole thing.

If you're on your own, you presumably have to hire an appropriate accountant.

This comes up even internally in the US if you're spending a lot of time in a number of states as a non-resident.