State immunity — Jurisdictional immunity — Employment dispute — Locally recruited chauffeur employed by mission of foreign State — Employee having same nationality as employer State — Claim for salary arrears and overtime pay — Whether foreign State entitled to jurisdictional immunity — Subordinate nature of employment — Relevance of fact that employee of same nationality as employer State — European Convention on State Immunity, 1972 — Extent to which Convention rules may be applicable to non-parties as evidence of generalized State practice — The law of Switzerland