Here's how it works:
I know the law of Australia, Hong Kong, China, and the U.S. However, I only advise clients about U.S. law.
Why? Because I'm liable for malpractice if I get it wrong. Unless I'm willing to religiously follow the legal developments of X other nations, I would not be willing to take the risk of the law having changed since I last check it. And if I were the kind of person anal enough to follow legal developments in other countries, my skills would be in such demand that only megacorporations could afford my services.
[0] http://www.nysscpa.org/cpajournal/2005/605/essentials/p54.ht...