Le Kef was right on the border of the North-South divide in Tunisia, which runs from here down to Sfax on the coast, about 100 miles to the south. The southern half is far poorer and also much more traditional. Headscarves start becoming a lot more common on women. Not everyone speaks French.
Whilst French isn’t universal in the North, almost everyone speaks it to some degree, and people who don’t speak any at all get teased by their friends. A lot of people are effectively bilingual, and switch back and forth, sometimes in the same sentence. By far the most common greeting in the North is “ ‘Assalama, ça va?” I’ve seen women admonish their child in French then switch back to Arabic to be more accommodating. At the very least, like nineteenth century Europe, it’s de rigueur to be au fait with French bon mots.