I think that the general approach on SE sites is to 'build the hive' rather than go looking for bees (so to speak). In that case, we shouldn't worry too much about reaching the target audience, but concentrate on creating an 'awesome site'.
But that still begs the question of awesome site for whom?
The proposal said:
For students, teachers, and linguists wanting to discuss the finer points of the French language.
So it should be clear, right? But I think the 'finer points' could be a bit difficult to define. And the thing is, whatever we may want, the initial audience is going to be an overwhelming influx of bilingual geeks from Stack Overflow. If that matters.
Maybe it's abundantly clear and I'm fussing for nothing.