Screenwriting : Bilingual Screenplay by Randy Steinlauf

I have an idea for a story that, by its very construction, will require the characters to speak in English while the protagonist speaks in French. I am fluent in both languages and could easily write it as I visualize it, but obviously the readers will almost certainly be only English speakers. So, my question is this: is the proper way to render the screenplay to write everything in English and simply add a parenthetical each time the protagonist speaks under his dialogue? Like this: (subtitled; in French).