A friend of mine had a TL idea years ago where the French revolutionaries deliberately identify the Ancien Régime with the "foreign" Franks, and identify the common people of France with the ancient freedom-loving Gauls, thus giving a cultural/linguistic dimension to the class conflict. The revolutionary regime institutes a policy of "re-Celticization," trying to bring back supposedly Gaulish customs and linguistic elements, while simultaneously de-Germanicizing the country's identity. As part of this, they develop a foreign policy that is particularly hostile to England and Prussia, sending even more aid to Ireland than in OTL for example. It would be cool to see it as a full-fledged TL, if it's something you were to feel like trying out
@Gloss
I confess that at first I thought "well, that's kinda far-fetched"... but then I remembered that the guys in charge of the French Revolution actually reinvented the calender, renaming all the days of the week, months, years, and restarted the reckoning of years, and directly undermined the power of the Catholic Church, and reformed law codes from scratch. They were serious business.
Also, another factor that might come in handy in this scenario: according to a teacher of mine who studied in France, until the French Revolution the "regional dialects" were pretty distinctive as far as one went farther from Île-de-France, with a rather substantial number of Languedoc, Gascon, Provençal, Breton and Flemish speakers. After the Revolution, the creation of state-sponsored public education resulted in a strong effort to "uniformize" the French identity, mainly by the enforcing the traditional French vernacular. I remember to have read, in fact, that until World War One, you could still find French soldiers in the trenches that had grown up learning their own regional language (mostly Langue d'Oc) than French...
In this alt-scenario, perhaps the Revolutionary public education system emphasizes the "de-Germanization" of the language, as yoy guys said. After some three or four generations, there would be a significant impact.