McDonald's work vocabulary is not that complicate because it has a limited menu and the interactions are mostly structured in the same way.

The thing is the accent for both, the guy behind the counter and the customer.

But remember that many people go to McDonald's and order their meal sometimes using just the number itself by looking at the pictures on the wall.

Any ESL/EFL book published in the last 10 years or so that teaches how to order food in a restaurant would be great for you to have so that you can teach your friend.

The idea about ordering and serving food is the same but understanding the accent is the main thing.