Referring the question to, Dr. Monzer Kahf, Islamic Economist & Financial Expert, he said,
A Last will in a Muslim country is essentially an expression of the person’s will of giving to charity and other worthy causes and persons within the limit of one third on the net estate (after payments of debt and expenses). In countries that have no mandatory Islamic family and inheritance laws the last will must contain in addition the order to distribute the remainder according to Shari`ah inheritance rules. Any person who owns a property should write a last will and is encouraged t do so if one does not live under Islamic inheritance law. Keeping in mind that husband and wife, each owns her/his property independent from the other, each one of them is encouraged to create a last will, or required to do that if she/he does not live under Islamic inheritance laws.