As I understand, when we say something about people from some country generally, we use the plural form. For example, "The Italians are people who have made their mark in many parts of the world." Here "the Italians" refers to Italian people in general.
Here are some of the results I found when I searched for
"the italians are",
The Italians Are Losing Interest in Wine (title of an article)
The Italians are said to be the most passionate people in Europe.
However, I also found a small number of usage of "the Italian is",
Like the Chinese, the Italian is a born gambler.
"You want to know why the Italian is skinny?"
The first was from the book How the Other Half Lives. Considering that the book was dated back from 1890, and the joke, well, is a joke, is this usage of the singular form for stereotypical people still acceptable in modern English?
(As a side note, I know that I should write the British, the English, the French, and other handful countries without -s or -es, and I must use them as plural.)