I'm bilingual, not in French and English, but in different languages, and I know what it means. You will never, ever be perfectly proficient in the two languages. I can tell you that my mother tongue is a different language, and I'm not proficient in my mother tongue.
Do people in our country have the opportunity to improve their language skills? Take the vérificateur général; can he improve his skills? If he doesn't perform in a language at a certain level, you should say, “Thank you very much and goodbye. Unfortunately, your services are not required anymore.”
Should we give him the chance to learn to speak the other language?