The majority of international academics working in France are from other Romance language countries. I presume the other Romance language countries have the same problem as France.
Language is not really that big of a factor. The U.S. definitely provides better research ressources but when you look at your life as a researcher as a whole, France is the better option.
In fact, English took from French over 30% of its vocabulary. French was the official language in England of the highly educated until mere centuries ago.
Most researchers in France already speak English.
The huge advantage of the US/UK is one: money, you could become rich and apply your ideas to real products(in a bigger market) much much more easily than in France.
The huge advantage of France: quality of life.