Of course it’s not actually international law. It’s a non-binding agreement between nations in a “club” that has no legal standing and Japan keeps threatening to leave.
Japan never signed the treaty so legally they are in no way bound by it. Something like the US never signed the "ICC" treaty so we are not bound by it.
And for some reason they never went after Norway or Greenland, who both still do whale hunts.
And Norway does not even eat their whales.
But hey it make people who have no idea of the difference between a narwhal, sperm whale, humpback whale or minke whale to run around spouting nonsense about the evil Japanese.