Within a third State, a person having more than one nationality shall be treated as if he had only one. Without prejudice to the application of its law in matters of personal status and of any conventions in force, a third State shall, of the nationalities which any such person possesses, recognise exclusively in its territory either the nationality of the country in which he is habitually and principally resident, or the nationality of the country with which in the circumstances he appears to be in fact most closely connected.