However, after a point of time the 33-year-old actress grew tired of speaking in her native language because she felt it was affecting her acting, reports The China Daily.
She said: "Johnny's French is excellent. But I could not let myself lapse into speaking a lot of pure French with Johnny. I was working so hard to really perfect the accent of my character Billie Frechette, and that was not easy. She was of mixed heritage - both French and Native American - and supposedly had an accent that was quite different."
Johnny - who lives in the South of France with his long-term partner Vanessa Paradis and their two children, 10-year-old Lily-Rose and Jack, seven - praised his co-star for her acting skills. He said: "Marion really worked hard on that accent, and I think the way she speaks in the film adds so much to the personality of the character she plays. You can see why Dillinger fell in love with her so easily."