SPEED is almost the only language in changing lanes

First we signal and maintain our SPEED to let other people know that I want to change lane;

Then after about 3-5 seconds, the vehicles in the other lane use their SPEED to talk to us, either speed up (no), or slow down a bit (yes);

And we may change our SPEED trying to create a safe gap based on their SPEED, if we can, we move in the other lane.

So, SPEED is almost the only language in changing lanes, apart from our signal light.