What is the remedy of a person who feels aggrieved by the acts of a foreign sovereign?

Under both Public International Law and Transnational Law, a person who feels aggrieved by the acts of a foreign sovereign can ask his own government to espouse his cause through diplomatic channels.

Private respondent can ask the Philippine government, through the Foreign Office, to espouse its claims against the Holy See. Its first task is to persuade the Philippine government to take up with the Holy See the validity of its claims. Of course, the Foreign Office shall first make a determination of the impact of its espousal on the relations between the Philippine government and the Holy See. Once the Philippine government decides to espouse the claim, the latter ceases to be a private cause.

According to the Permanent Court of International Justice, the forerunner of the International Court of Justice:

By taking up the case of one of its subjects and by reporting to diplomatic action or international judicial proceedings on his behalf, a State is in reality asserting its own rights — its right to ensure, in the person of its subjects, respect for the rules of international law. (The Holy See vs. Rosario, G.R. No. 101949, December 1, 1994)