You may be right. It's certainly a device that gets used in movies.

My own impression is that this is where Michael starts throwing off the passive role he's been handed. He's gotten into a car where he's outnumbered, endured a little pat on the shoulder from McCluskey, been frisked, and subjected to the Jersey maneuver. And he just had to sit and take it. So, switching to English is where he stops being passive, forces Sollozzo to yield a little control, and starts building the adrenaline he's going to need to kill the other two.

I don't think either of the Italians are giving McCluskey much consideration at this point. They've taken their measure of him, and decided that he has no personal force.