Having been an expat for a large portion of my working life I have done quite a lot of research into this subject. Probate and inheritance laws are different in every country and in some cases different jurisdictions within the same country for example Jersey has a different set of laws to the rest of UK.
If you asks a lawyer for advice on this subject you are unlikely to get any clear answers. You will be given the options that will make them the most money. In my experience these complex laws are conjured up to keep lawyers in business hence this whole arbitrary set of rules.
Following my research my deductions are as follows. If you have assets in multiple countries the ultimate answer is to place them all in an international trust however this can be quite expensive as far as set up and administration costs go. The second option is to have a valid will for each country and jurisdiction in which you hold assets. Whilst cumbersome this is the route I have gone down including a will drawn up by a Thai lawyer, translated and attested. To rationalize things a bit I am in the process of consolidating all of my assets into just two jurisdictions.
On a positive note if one’s assets and distribution wishes are not complex western countries mostly have a number of online will drafting services available and generally one only needs to have the will witnessed by two independent witnesses who are not beneficiaries.
If you go down this route to save your heirs some serious headaches make sure that the witnesses are likely to be easily located or traced should probate be required.
Ideally unless one wants to be a benefactor then the total sum of all assets should be zero on our last day on earth which would nullify this whole process, however seeing that none of us know when that day is it’s quite hard to plan for.