State immunity — Jurisdictional immunity — Language teacher employed in consular section of embassy of foreign State — National of employing State — Contract of employment — Dismissal — Claim for damages for breach of contract — Whether foreign State entitled to jurisdictional immunity — Whether fact that employee a national of the employing State is relevant — Relevance of European Convention on State Immunity, 1972, Article 5(2) — Whether applicable as codification of customary international law even though defendant State not a party — The law of Belgium