If you should die owning real estate property 'immovable' property (so boats are not included in this!) the type of property must be dealt with through the probate system of the country where it is, known in legal jargon as the 'lex situs', (if you have done latin at school you will understand the meaning). The term 'immovable' in this context means exactly what you would expect, assets that are stuck to the ground! So, houses, flats, blocks of land, anything to which you have a title.
If you have bought your flat or house in say Hong Kong, then Hong Kong probate rules apply and Hong Kong expects to supervise the change of ownership, either to the beneficiaries or to the Trustees of the trust fund set up in your Will. Likewise, if you also buy a house in Australia a Will must go through the probate system there. If you only have one Will then delays are likely because the same Will has to be probated twice in some states, and therefore it takes longer for the estate to be wound up
A grant of probate issued in Hong Kong is accepted in the UK, Sri Lanka, Singapore, New Zealand, Tasmania, Northern Territories, Victoria, and South Australia, but not in ACT, Western Australia, Queensland or New South Wales, or anywhere else in the world. The UK will accept a grant of probate issued in its old colonies, since the legal system was set up as Common Law and is therefore considered sound. At least, there are no major discrepancies as there would be for example with Spain or France, in both of which the legal system is Civil Code.
To put it at its most basic, Common Law is a system that is 'for the people', so a judicial system that involves a jury as well as a judge and allows the individual to leave his assets to whom he chooses (given certain restrictions for supporting dependants. Civil Code imposes the wishes of the State on its citizens and, as far as inheritance is concerned, it may dictate who has what in a family if someone dies (known as forced heirship). Many European countries are Civil Code, and so of course are the colonies of France and Spain and Portugal.
Many of the little Islands in the Pacific (British Virgin Islands, Cayman Islands, etc) are Common Law. So basically are most of the States in the US, but 3 in the South were originally French property and retained their original legal system after they were sold to the British, and of course in Canada Quebec is still very much Civil Code!
You can see from all this that to have one Will and property overseas, especially if it is a Civil Code country, is asking for trouble.
It is perfectly possible to have more than one Will. Each Will must be restricted to the country and type of property it is intended to cover and the drafting of such Wills needs to be done very carefully. At all costs one Will must not accidentally revoke another. In the long run the cost of complications and subsequent lawyer's fees in sorting out the mess far outweighs the cost of having Wills prepared as 'sets' of documents. There is less likelihood of serious errors creeping in if the whole process is done either by one person or supervised in some way. Many home-based small law firms are unfamiliar with this situation and will not deal with the overseas assets of a client, preferring to handle only that with which they are familiar.
If you are investing in property, do give this some thought. If you have a family that includes children under 18, then the delays could cause serious inconvenience for your spouse, and even worse for children left in the care of Guardians if both parents die.