I'm A Russian vs I'm Russian :)
Could you tell me whether it's correct to say 'I'm a Russian' instead of 'I'm Russian' or not?
I'd say that the use of "I am a Russian" could be used when it's an important fact for the ongoing conversation, or if there's something specific about being a russian person.
"I'm Russian" instead would just simply state your nationality.
That's my thoughts :)
In SE Pa. American English both are fine and correct to say. As Paul says, one "Russian" is a noun; the other an adjective. Your choice might be determined by whether you, consciously or unconsciously, wanted to emphasize your citizenship/nationality/type of person (the noun) or your qualities (the adjective).
"I'm an American," brings to my mind connotations of citizenship and belonging to a particular country or nationality.
"I'm American," sounds more to me like a reference to cultural qualities or characteristics.
So, I could say something like, "I'm an American, but I'm not very American," if I wanted to say that I was a U.S. citizen, but don't conform to the ways of thinking and behaving of the majority, mainstream culture.
The difference is subtle, and depending on the context, the native-English-speaker/hearer, might not even notice that you have said one (I'm a Russian) vs. the other (I'm Russian).
The first is the noun - so I'm a Russian person.
The second is the adjective, describing the nationality as in a Russian doll.
What is correct will depend on the context and what you want to say: the same happens in all the Romance languages.
I noticed that ethnic Russians (educated ones, obviously) in the United States prefer to say: "I am a Russian." It clearly defines a person's ethnicity. Which is important specifically in America where "Russian" is usually associated with anyone from republics of the former Soviet Union.
I used to say "I am a Russian." Very few Americans see the difference. But some do.