State immunity — Jurisdictional immunity — Employment dispute — Locally recruited employee of mission of foreign State — Employee having nationality of receiving State — Dismissal “for security reasons” — Claim for severance pay — Whether foreign State entitled to jurisdictional immunity — Relevance of failure of employer State further to specify grounds for dismissal — European Convention on State Immunity, 1972, Article 5 — Extent to which Convention rules may be applicable to non-parties — Whether enquiry into justification for dismissal would infringe sovereignty of foreign State — Scope of duty of foreign State to give reasons for dismissal — The law of Austria