Updated: Feb 8, 2023
If you have estates in multiple countries, managing the estates effectively is utmost important, you do need either International Will or Multi-Jurisdictional Will depending on the locations where your estates are. There are many reasons, however you may not realize until look at history that deceased persons have slapped with huge cost due to issues of Domicile, Revocation of the Will, conflict of laws, Signatory on the Will etc. in the different jurisdictions.
Domicile vs residence: i.e. Since the definition of Residence vs Domicile is different in different countries, it create complication in terms of taxes as well as implementation of Will when you have estates in multiple countries.
Revocation of the Will: i.e. you revoke Will in one country will revoke all other Wills made in other countries due to Will drafted not properly.
Conflicts of laws: between different countries i.e. every country, province, state or territory have different laws which create conflicts if there is no separate Will for each locations.
Signatures on the Will: with reference to time and locations. Testator and witnesses sign the Will in one country location. It means the country in which you have signed the Will may not have any jurisdictional issue, however if Jurisdictions outside the country or province may not accepts the signatory. Jurisdictional law may differ from country to country, state to state, province to province or territory to territory.
International Will: Your first option is the International will obviously if you have estates in multiple countries which are part of signing the "Uniform law on the form of International Will, Washington D.C. 1973 enacted by UNIDROIT.ORG". It requires authorised persons to Witness and Sign the Will. In most countries, the authorised persons is either lawyer or recognized lawyer association body. So you need to consult lawyer for creating International Will. Lastly, the Will has to be registered through International Will representative office and usually taken care by lawyer or you can register yourself by visiting office or sending them through by mail.
Countrywide Will: Majority of people create the Countrywide Will but there are things needs to be considered. If you are creating Countrywide Will then you may create one Will for multi-jurisdictions, IF AND ONLY IF there is no issues with Domicile or residence, Conflict of laws, Signatory on Will etc in acceptance among the countries where your estates situates then you can create one Will based on religious or cultural law.
Multi-Jurisdictional Will If that is not the case then you have no other option than creating Multi-Jurisdictional Will.
Faith based Will: If you are creating Wills based on religious or cultural laws then you may create one Will for multi-jurisdictions IF AND ONLY IF there is no issues with Domicile or residence, Conflict of laws, Signatory on Will etc in acceptance among the countries where your estates situates then you can create one Will based on religious or cultural law.
UNIDROIT.ORG website -International Institute for the unification of the private law. Go to Successions under Instruments for more information. For latest status on which countries are part of convention, visit UNIDROIT.ORG, Go to status-successions.