Please tell me to what problems this can lead or how safety is compromised in a dual language ATC airspace.
I seem to recall an incident in the last five years when CDG ATC cleared a BA aircraft that had landed on 27R to cross 27L in English, into the path of an Air France that had been cleared for take off on 27L in French. Fortunately the technology in the tower alerted the controllers to the conflict and the AF340 was instructed to abort it's take off. I would suggest that's an indisputable example of dual language compromising safety.