International law is a complicated mess, and I doubt any forum moderator is going to be an expert on it. The forum owners might know something, since they would be the ones to set overall policy, but even they could not predict every possible scenario.
Here is the Wikipedia article on Defamation, it has a section about international laws. Short of consulting a lawyer, or spending considerable time in research on the specific countries involved, I doubt you're going to find good answers. An since law is always being challenged and changed, especially international law, you could end up being sued anyway.
In the end, it is simply best not to go around bad mouthing people without proof. You can't be sued for what you don't say.