Sovereign immunity — Foreign States — Germany-Romania Population Transfer Agreement, 1940 — Obligation upon German Reich to pay compensation for loss of property consequent upon resettlement — Claim by private individual for payment of compensation — Whether Federal Republic of Germany entitled to jurisdictional immunity — Acts iure gestionis and iure imperii — Whether treaty obligation to pay compensation to individuals governed by private or public law — Whether such obligation a matter for legislation — The law of Austria