Just like different US states have different rules about what it takes to make a writing a valid will, different countries have different rules regarding what it takes to make a writing a will. For individuals who reside in a country other than their country of citizenship or own property in another country, these differences can create major headaches when it comes time to probate a will.
In order to prevent just those type of headaches, the 1973 Convention providing a Uniform Law on the Form of an International Will provides for unified requirements to cause a writing to be valid in any signatory country. Following these requirements allows for a one-document fits all affected jurisdictions approach to drafting a will, assuming all the jurisdictions are signatory countries. The convention is a great help for those living in an increasingly globalized society and can be found at http://www.unidroit.org/english/conventions/1973wills/1973wills-e.htm
However, because probate law is ruled by the states and not the federal government, the benefits of this treaty only clearly apply to residents of those states which have adopted the provisions of the treaty into their probate code. Luckily for Minnesota residents, Minnesota has adopted the provisions in Minnesota Statutes 524.2-1001 et al.
Some of the major additions to a normal will that are requirement for international wills, is for each page to be numbered, for each page to be signed by the testator, and for the will to be witnessed by an "authorized person" in addition to the standard witnesses required under state law. An "authorized person" in Minnesota is anyone licensed to practice law in the state of Minnesota.
If you reside in a country and have citizenship in another or have property in other countries, speak with an attorney licensed in your jurisdiction of residence who has experience with international wills.