There's also several times in TNG when French is referred to as an archaic language. Picard was fluent, but even he gave himself away as a nonnative speaker despite actually growing up in France. It doesn't appear to be because humans have chosen a unified language, either, since several characters like Chekov have vocal quirks that give them away as nonnative English speakers, so at least some non-English languages are still in use.
Whatever happened to France, it was fairly recent, very late 23rd Century or first half of the 24th. It was still a contemporary language in Enterprise, and there was a French-speaking colony in TOS.
I remember a scene in the german version of one the first episodes of Enterprise Captain Archer tells some alien that humanity actually speaks german. There you have it.