The state that built a language also suppressed half a dozen others — and the constitutional tension has never quite resolved.
France recognised its own languages late and reluctantly

The nation built itself on one tongue
When revolutionary deputies in 1794 sent the abbé Grégoire's report on the "patois" of France to the National Convention, they were not describing colourful local variety — they were diagnosing a problem. Grégoire's survey found that perhaps three million people spoke French well enough for civic life, out of a population of nearly twenty-eight million. The rest spoke Breton, Occitan, Alsatian, Basque, Flemish, Corsican or any of a dozen other tongues. The prescription was elimination, not accommodation: the revolutionary state saw linguistic unity as inseparable from political unity, and schools would be the instrument.
The policy did not take hold overnight, but the Ferry laws of the 1880s — which made primary schooling free, compulsory and secular — turned intention into mechanism. Teachers in Brittany, in Languedoc, in Alsace (when France recovered it after 1918), in Corsica, enforced French as the only language of the classroom. Children who spoke Breton in the playground were sometimes given a token, the symbole, to pass on to whoever they heard next speaking the local tongue — a device that automated collective shame. By the mid-twentieth century a generation had grown up understanding that their grandparents' languages were backward, rural and professionally useless.

The constitution's awkward sentence
The turning point, such as it was, came late. The Deixonne Law of 1951 was the first legislation to permit regional languages into state schools at all — and it was tentative: a few hours a week, optional, covering only Breton, Basque, Catalan and Occitan. Alsatian, Flemish and Corsican were excluded. Corsican was not added until 1974, Alsatian not until much later.
The deeper problem is constitutional. Article 2 of the French constitution states that the language of the Republic is French — a clause added in 1992, partly in response to the Maastricht Treaty, to head off any suggestion that European frameworks might dilute it. In 1999, France signed the European Charter for Regional or Minority Languages, which would have created enforceable protections. The Constitutional Council ruled that ratification would require amending Article 2, since the charter's protections for minority languages could conflict with the principle of a single national language. The charter has never been ratified. France remains one of very few European Union states that has signed but not ratified it.

The 2008 constitutional revision did add a new sentence — Article 75-1, stating that regional languages belong to the heritage of France — but heritage is not the same as right. Heritage is a museum concept. The languages are acknowledged; they are not co-official.
What survived and how
That any of these languages survived is partly despite the state and partly because of determined cultural movements that accelerated in the 1960s and 1970s. Occitan had an organised literary revival stretching back to the Félibrige movement of the nineteenth century, led by the poet Frédéric Mistral. Breton had immersion schools — the Diwan schools, founded in 1977 — which exist in a legal grey area, privately run but partially state-funded, and which produce children who are genuinely bilingual. Alsatian survived in a different way: the particular history of a region that changed nationality twice in a lifetime meant that German dialect and French sat uneasily beside each other, both with official pressure behind them at different moments.
Corsican is estimated to have perhaps a hundred thousand regular speakers out of a population of roughly three hundred thousand, though estimates vary. Breton's active speaker numbers have fallen sharply across the twentieth century and are now concentrated among older generations, though the Diwan schools represent a small but real reversal. Occitan's situation is particularly complex, spanning not just southern France but parts of Italy and Spain, and divided into dialects whose mutual intelligibility is debated.
None of this resolves neatly. A child in Quimper today can receive part of their education in Breton; the same child's grandparent may have been punished for the same act. The state has moved, but it has moved carefully, keeping one hand on the sentence in Article 2.