Hi, it would help if I knew which country you were in, but here's an illustration if it helps (I'm a lawyer and run a will writing business)
It basically depends on two things, where you are domiciled and what type of property you own.
So say you are domiciled in the UK, ie you were born and brought up here and intend to return here at some point but are on a 5 year or even longer contract in, let's say, Hong Kong.
Let's assume you own a flat in HK and a house in the UK which you're renting out. We'll call those your immoveable assets.
Let's also assume that you have bank accounts, shares and other moveable assets in both countries. Those are your moveable assets
Because you see the UK as your home and will come back here at some point, you have domicile in the UK. That means that you can make a Will in England and Wales which will cover all of your assets anywhere in the world except for your flat in Hong Kong.
You would need to make a separate Will in HK covering just that flat, and ensure that the two wills did not cancel each other out. Your will writers will need to be made aware of the existence of the other will and word their revocation clause accordingly. They would need to arrange for storage of their wills with a copy of the other will, to be read in tandem.
Other than that, your wills wouldn't be that complicated.
If, however, you aren't domiciled in England and Wales, you'd need to seek advice from a solicitor in your host country.
If you are domiciled in E&W, feel free to give me a shout. I have a paid for advert over on the Small Business Section of Mumsnet Classifieds.