I play on Moogle, and yes there are a lot of French players. It's not the majority, probably something like an 70/30 split or roughly along those lines. It's not a problem though, as a large number of French people can also speak English perfectly well. Infact, most of my current static happen to be French, and they all speak perfect English.

Don't let nationalities decide where you want to play. Create a character on every world and see where you like the most.