Perhaps I can relate my own personal experience. Before joining the public service, I spent most of my career as a professor at McGill University. I'm obviously a francophone. I was doing work in molecular genetics. I submitted my grant applications in English, because I did not have the support from my institution to translate my grant applications into French.
The reason I was writing them in English was simply that all of the products that were coming out of my research lab and my research group—by products I mean publications and theses—were in English. I would copy and paste and assemble the grant application because the products were available to me, and I did not have support from my institution to operate differently.