That might indeed vary from country to country, yes, but from what I know, the requirements are quite lax all around the globe.

In the EU, food supplements share the same regulations as regular food. A problem arises when there's no regulation for a compound in regular food - even if it's just because there is no realistic szenario where concentrations can be reached that are high enough for the compound to exert toxic effects. So even if that might happen with supplementation, the compound remains unregulated. That's exactly the case for isoflavones. So even as soy isoflavones are more or less marketed as a kind of natural drug, the are regulated (or rather not regulated) as a food compound.

In the US, consumer protection is usually weaker than in the EU, so I wouldn't expect much regulations on supplements either.