I think that the real problem is : how many passengers don't understand the language spoken by the cabin crew when they make the safety briefing ?
I recently flew Charleroi-Pescara on an OnAir flight flown by Blue Air.
The safety briefing was made in heavily Romanian accentuated English, when most of the passengers spoke only Italian and/or French or Dutch.
How many of them understood the briefing ? I am prepared to bet : not one in ten. And, quite naturally, they stopped listening after the first sentence ...