Historically France was a patchwork of regions, you could even say countries, with different languages. In the later Middle Ages, someone would typically only think of the area around Paris, the Ile de France, as France. The lower part of the "hexagon" of the country was dominated by various dialects of what's now called Occitan, which is not too different from Catalan. It covered a very big area- Provence, Limousin, Gascony, Béarn, Vaucluse ( and I am probably forgetting another few). It was/is very much a language in its own right ( though it does seem sometimes to be a cross between Spanish and French) and had a literature- all those Troubadors were singing it at the court of Eleanor of Aquitaine. Here is a book that has parallel French and Occitan text, if you're curious. It's about the regional instruments of drum and one-hand flute.

In the 19th century France became more centralized, and there was a push to make French the standard thing to speak. Kids speaking in Occitan ( or Breton, other languages) would be punished in school. But there was a reaction against that in the 20th century, and now there are people who make a point of being able to speak it, and about being Occitan, just like there are Bretons who are fiercely proud of being and speaking Breton in Brittany. There's a great little book by Graham Robb, called The Discovery of France, which talks about the variety of cultures there.