反対側から乗って！って英語でなんて言うの？

It's always good to use please so that you don't seem rude. "the other side" is how we refer to the sides of cars. I hope that this helps. :)

Saying "Please get in on the other side" is a polite way of letting the other person know that they should use the door on the other side of the car. "Please use the other door." is another way of saying this, and is still polite but a little quicker and a little less direct (I would say this if there was only one other door; no back doors, or it might be confusing!)

Different countries drive on different sides on the road and some cars the steering wheel can be on either the left or right so can be confusing therefore you would say 'can you get in the other side?' or 'please get in the other side'

In natural speech, the listener knows which side you will be referring to from where you are standing. Here are two common sentences you can say if you want them to go to a different side: 1) "Please go around to the other side." - This means you would like the person to walk around to the other side. If you need them to come to the side you are currently on, then you can say, "Please come to this side." 2) "Please sit on the passenger/driver's side." - This lets the person know the exact side he or she needs to go to.