Belgium has ratified the Hague Convention of 5 October 1961 on Conflicts of Law relating to the Form of Testamentary Dispositions.  That means that Belgium recognizes Wills drafted outside Belgium if they are drafted under your national law, or under the law of your country of domicile or residence, or even under the rules of the country where you own real estate.

The Hague Convention has also been ratified by Antigua and Barbuda, Australia, Austria, Bosnia and Herzegovina, Botswana, Croatia, Denmark, Estonia, Fiji, Finland, France (including its overseas territories), Germany, Greece, Ireland, Israel, Japan, Lesotho, Luxembourg, Mauritius, the Netherlands, Norway, Poland, Serbia and Montenegro, Slovenia, South Africa, Spain, Swaziland, Sweden, Switzerland, the former Yugoslav Republic of Macedonia, Tonga, Turkey and the United Kingdom. Italy and Portugal have signed the treaty but have not ratified it. Check the website for the list of countries that have adopted it.

Please keep in mind that a foreign Will needs to be translated into one of the official languages (Dutch, French or German) and "translated" in terms that are consistent with the Belgian rules that protect certain heirs (see hereinafter.