For example.. states:
A licence issued by any other ICAO Contracting State (including a JAA State that has not yet been recommended for mutual recognition) is also deemed to be valid under the ANO for the purposes of flying a UK registered aircraft, providing that the licence and medical are valid in accordance with the rules/laws of the issuing State, and the CAA does not in the particular case give direction to the contrary.
Or...
Validation of Foreign Licenses
1. The Convention on International Civil Aviation, often called the Chicago Convention, provides for world-wide recognition of flight crew licences issued by any member State of the International Civil Aviation Organization (ICAO) provided that:
a) the licence meets or exceeds the ICAO licensing Standards of Annex 1 (Personnel Licensing) to the Convention on International Civil Aviation; and
b) the licence is used on an aircraft which is registered in the State which has issued or validated the licence.
2. If the licence is to be used on an aircraft which is not registered in the issuing State, the licence holder must obtain a validation of the licence from the State of Registry or alternatively obtain a new licence issued by the State of Registry on the basis of the original licence. The Convention on International Civil Aviation and its Annex 1 do not provide for the validation of licences. As a result, conditions under which validation is granted vary from State to State. It depends on the level of privileges required and on the origin of the licence. It is generally easy to obtain a validation for VFR private flights, but more stringent rules may exist for professional licences. The applicant may be required to get additional training and/or to take new exams. As an alternative to validate a foreign licence, a State may issue a licence which is based on the foreign licence held by the applicant. The condition for the issuance of this new licence is generally similar to that of a validation.
3. ICAO is unfortunately not in a position to provide information on the details of the validation procedures established by each of its member States. The most reliable source of information is the Licensing Authority of the State in which the licence is to be validated, and at times Consulates and Embassies may be helpful.
PW