So the Justice Against Sponsors of Terrorism Act (JASTA) happened. That leads to some questions. In a typical legal suit, a nation's courts would handle it, and the ruling would be enforced by the military/police/governing body. It is through the power of government that it's courts have the authority to rule on disputes.
On an international scale, historically "Authority" has been "Military". While I certainly hope that JASTA doesn't say "any sovereign nation that refuses to pay up to a private citizen will be considered in contempt of the US and military action will be taken", I can't think of any other solution to how to enforce JASTA rulings.
On top of that, in a citizen against citizen legal suit, the Jury is required to be an impartial Jury of peers. I doubt that any court within either nation on a side of the dispute could be considered impartial. Other nations would have to be willing to hear cases, so how could only a US bill alone accomplish this?