It probably varies from one part of Belgium to another. The northern half of Belgium (Flanders, Brabant, etc) is Flemish-speaking (usually called Dutch) and the southern half (Wallonia) is mostly French-speaking and in Brussels they speak both languages. A large proportion of the population (but fewer than in the Netherlands) can speak English. I have only visited Flanders in recent years; it is a flat country with fields canals and rivers between the towns. Most of the towns are quite compact; many have historic centres. Small shops and markets abound, more so than in Britain.
You should be able to buy most ingredients for your cooking, with or without meat, but you might have to travel a mile or two before you find a good selection of spices or tropical-style
fruit. You will probably find there are parts of town where Indian-style food can be bought easily, and other areas where it is hard to buy.
Whenever we have been there, we only found one type of food difficult to buy: fresh milk. Most shops only seem to sell UHT (

) milk.