Every eligible person registered in the consular register of a Belgian embassy or consulate can register to vote. This doesn’t happen automatically; for every election you’ll need to confirm how you want to vote: voting personally at a Belgian commune or a diplomatic/consular office, voting by proxy at a Belgian commune or a diplomatic/consular office or voting by mail. The right to vote for Belgians abroad is limited to federal elections.

Contact your embassy or consulate for more information about elections abroad.

Sources:

https://www.vlaanderen.be/nl/vlaams-parlement/verkiezingen/stemrecht-en-stemplicht-bij-verkiezingen/kunnen-belgen-het-buitenland-deelnemen-aan-verkiezingen-belgie

https://diplomatie.belgium.be/nl/Diensten/Diensten_in_het_buitenland/Deelname_aan_verkiezingen/Belgen_buiten_eu