In most cases, civil servants are required to respond to any inquiry in the local official language, meaning either Flemish or French. This includes the local municipality and CPAS services. Be aware that once you are a resident and need to make a request at the commune or CPAS, translators are not allowed to help you and you need to be able to communicate on your own in a language that is understood in Belgium because those bodies expect you to put efforts into learning the local language.