French summer courses in Brussels for an adult
You can find plenty of options by googling French language courses brussels. There is an overview at https://www.brussels.info/language-schools/
If money is no object, I did a 3 week intensive one to one course (4 different teachers, alternating during the 6 hour day) in my twenties. Immediately after those 3 weeks I lived in France for 3 months in a situation where I was using French every day. It took me from very bad GCSE level to a very competent level. You need to practice, watch French TV and listen to French radio.
Have you found a solution for your summer course? Hello Languages may be able to help you depending on what you’re looking for. I work there :)
Feel free to get in touch: firstname.lastname@example.org