The Pope isn’t a world leader. He is the head of the Catholic Church on earth.
I know you mean “not leader of a country” but the head of the Catholic Church is a definitely a world leader. He has huge influence and other world leaders work very hard for good relations with the Pope.
Even if you really, really, want to specify, “leader of a country”, the Pope is still included. He is the the absolute monarch, head of government and head of state of the sovereign state of Vatican City State.
Anyway, back to the original question. I would come up with some human rights guidelines prerequisites and consistently apply them. It would take time to draw the rules, but I know for sure a lot of current American “allies” would not make the cut.