Common language is always needed - this is CDG, a large airport with many flights. It is important that all planes have situational awareness. If half are speaking French, how does the pilot coming from Seoul have situational awareness? What if he's sitting on the runway and doesn't know that the ATC just gave clearance to land in French to a pilot on the runway he's currently on?

ATC and pilots for commercial airlines should only be speaking English, regardless of their native tongue and where they are.

It's pretty important - and it is actually EU law: https://www.thinkspain.com/news-spain/29531/air-traffic-cont...

Unfortunately it only applies to airports with 50k international flights per year - the bar should be much lower than that. But of course, CDG qualifies.