What are some interesting differences from country to country?

This may be too vague, but potable water, is frequently an issue in many places.
If you’re in a country where you have potable tap water, you forget what a luxury it is.
And not avoiding the wrong water, has potentially life threatening risks.

Traffic rules of the road..
What is considered rude/polite.
Construction codes.
Judicial procedure.
Vacations/holidays.
Foods.
Alcohol laws/guidelines.
Penal codes.
Medical care.

Intelligence levels of people who would vote for Trump.

In the U.S. and England, some words that are spelled the same, and have the same meaning are pronounced differently, such as laboratory, garage, can’t, issue.

And then some things have different terminology for the same thing such as water closet and bathroom; boot and trunk; flat and apartment; motorway and freeway.