Are you looking for mat pilates or reformer-type? I was a reformer pilates devotee, and had trouble finding one I liked (pilateszone in Enge has at least one English speaking class a week, but you have to commit to going to the same class every week, which was hard since I travel so much for work). I started going to www.boosterpilates.ch
near Wiedikon - which uses a 'megaformer' - all their classes are in English, they have like 10 a day, and you can buy a bundle of classes and go to any of them. Your first class is free, so definitely worth trying out if machine pilates is your thing!