Yes. The French stole the Rosetta from the Egyptians and the English stole it from the French. It's still in the British Museum today and I've heard no reports of Egypt objecting. But I don't think that will be the case, if one of these Japanese collectors is stupid enough to show off one of his trophies from Afghanistan. There is also the possibility of blackmail by the thief who fenced it to him.
The Rosetta Stone is just a mundane legal document... in three languages.