Applicable National and International Requirements
ICAO, EASA and national authorities
The 1944 Chicago Convention created ICAO and its 19 Annexes. The ones most relevant to maintenance are Annex 1 (Personnel Licensing), Annex 6 (Operation of Aircraft), Annex 8 (Airworthiness of Aircraft) and Annex 19 (Safety Management). SARPs are implemented by States through national law; ICAO itself issues no licences and approves no organisations.
Article 33 obliges States to recognise certificates issued by another State provided they meet or exceed the minimum standards; Article 83 bis allows transfer of certain State functions to the State of the operator. Where a State cannot comply, it must file a difference with ICAO.
At regional level, EU regulations are directly applicable in Member States (2018/1139, 1321/2014, 748/2012, 965/2012). EASA is an agency, not a State, and does not hold a national register. Third-country licences, parts and approvals may need validation, or may be accepted under a bilateral agreement such as a BASA.
Traps: quoting Annex 8 as the operations annex (it is airworthiness); assuming ICAO approval exists; forgetting that national authorities issue the licences and approvals; ignoring that a licence from a non-EU State generally needs validation before certifying EU-registered aircraft.
Worked example: a mechanic with a third-country licence applies to work in an EU Part-145. The organisation cannot simply accept the foreign licence - conversion or validation through the NAA under Part-66 rules is required before an authorisation can be issued.