If you need a sign language interpreter, you have to provide one yourself, unless the organising party is responsible for this and has made arrangements beforehand with Tele Ticket Service, the actual organiser or the people in charge of the venue (for example, by booking seats and providing a temporary hearing loop).
Stadsschouwburg Antwerpen has a permanent hearing loop for the hearing impaired. It concerns seats on the ground floor from row 7 to row 24, including side blocks. The frequency is 'T'.
Read also: How do I reserve tickets for visitors with specific needs?