I think the indefinite article adds emphasis. (I’m definitly not a grammar expert but I’m German.) He not just somehow happens to be a Berliner, he affirms to be a Berliner.
(I have an alternate hypothesis: like all Germans I heard that sentence a few dozen times, saw it again and again repeated on TV. Maybe the sentence just made that usage correct by sheer force of its existence. I would say that’s unlikely, but it’s possible. What I’m sure about, though, is that everyone who listened to JFK knew what he wanted say.)
Is it perhaps the same difference as between "I am English" and "I am an Englishman"?
Presumably you'd need to be a true bilingual to tell if they feel the same, and even then, your thought processes aren't going to be the same as either type of monolingual.
> Is it perhaps the same difference as between "I am English" and "I am an Englishman"?
Yes, that's a very good analogy.
If you say "Ich bin Berliner", it just means that you live in Berlin. I doesn't put any emphasis on identifying with a certain group of people. It merely says that you belong to this group, maybe just by accident.
However, if you say "Ich bin ein Berliner", especially in the context of his speech, it means that you identify yourself with the group, i.e. with the people of Berlin.
That's why I disagree with that point of the Wikipedia article. "Ich bin ein Berliner" was a perfect formulation. I guess Kennedy got the help of a native German speaker or had a very good translator.
This is so opposite to the view that we were all taught in North America (namely that Kennedy's statement was a gaffe that made him a laughingstock) that I wonder how the misconception even arose. No one ignorant of German would have come up with the idea that JFK said he was a jelly doughnut, but from what you guys are saying, no one who knows German would have thought that either. Perhaps it was clever Soviet disinformatsia!
(I have an alternate hypothesis: like all Germans I heard that sentence a few dozen times, saw it again and again repeated on TV. Maybe the sentence just made that usage correct by sheer force of its existence. I would say that’s unlikely, but it’s possible. What I’m sure about, though, is that everyone who listened to JFK knew what he wanted say.)