It's a very simple question, but I feel puzzled for some reason.
I am Russian. They are... Russian or Russians? (Some people from Russia are meant here.)
He is Greek. They are... Greek or Greeks?
I would say "They are Russian/Greek/English/Portuguese". Should I use the adjective (Russian) or substantivized adjective (Russians) in sentences like these?
Please correct me if I am wrong.
"Russian" is both an adjective and a noun.
You can say "these chocolates are Belgian" or "my friends are Belgian" - both times you use the adjective to describe the chocolates or the friends.
You can say "my friends are Belgians" but not "these chocolates are Belgians" - "Belgians" is the plural of the noun "Belgian" which means "a person who is a citizen of Belgium". The chocolates are most definitely not citizens of Belgium, so "Belgians" is wrong there.
You can say "my friends are Russian" or "my friends are Russians" - once it is used as an adjective, and once it is used as a noun. Both ways are correct. The meaning is practically the same.
It depends on the context. "Russian" would be used if generically you mean that the people are associated with Russia, either actually being from Russia, having Russian descent, etc.
In contrast, "Russians" would be used if specifically you mean that the people are from Russia.
The same could be said for "I am Russian" (generally speaking) as opposed to "I am a Russian" (specifically making the point that you are from Russia).
The same goes for many other nationalities, e.g. for "American" if some Americans were in France you could definitely imagine "they are American" being said, since it's true that they're American, or instead "they are Americans", pointing out specifically that they are from America and emphasizing that they are foreigners.
You are correct, to describe several people who are from Russia you would describe them as being Russian.
"Those people are Russian" "They are Russian"
However if you were describing what they are doing as apposed to who/what they are, and addressing them as a group, the word Russian would change to "The Russians are very happy here". This is the case only with Russian, if you were to use any of your other examples they would always remain the same, "The English are very happy here/ They are English", "The Greek are very happy here/ They are English".
Ah the English Language so complex! All the best.
