Floating islands are in a way, still a ship. Once a ship is 24 miles from any coastline, it's on the high seas (or international waters). With the exception of certain rights within the contiguous zone, the law of that ship is the law of the country whose flag it's flying. Right?
That's right, and as far as I understand they are planning to stay within the French Polynesia areas during several first years at least, which means that the laws of the French Republic will be applying to them. I personally don't believe they can make it to an independent state, but I wish them all the best with their aim because the world is funnier place to be when there are more different countries.