I had never heard or seen ổn before... Is it a specifically northern expression?
"I'm fine" is generally "tôi khoẻ" or "tôi bình thường" in the South. "Tôi ổn" also makes sense.
Agreed....I live in the South....Tôi khoẻ was one of the first things I learnt. I'd never heard "tôi ổn" until this lesson.
That may be the case. But I'm certain it's used in the south too. Perhaps you can't hear it because Vietnamese people don't tend to ask "how are you-I'm fine" to start a conversation.
I was told by my parents/older sibling that it's not specific to a dialect/region, just that you might not really hear it spoken that often. But my sibling has seen it in books when learning, growing up in Vietnam.
Is it normal that I don't hear the dấu hỏi on the ổn when the duolingo voice pronounces it?
Yes, that's normal. The speaker is from Hanoi, where the hỏi tone is usually not pronounced in a dipping (falling-rising) way, but just falling. The difference to the huyền tone is really subtle.
Is Vietnamese one of those languages that allows you to drop the copula ("là" in this case) or is it that "ổn" is just expressed without là?
Neither. Vietnamese is one of those languages without adjectives, like most languages in Southeast Asia. Ổn here is a (stative) verb, meaning "to be fine", so it doesn't need a copula.
Also, Vietnamese does tend to drop as many words as possible without (too much) altering the meaning of a phrase... Copulas are usually not really instrumental to the comprehension of a phrase so they are very often dropped. But classifiers also often suffer the same fate. :)
Not in this case, though. You can't say Tôi là ổn, I think. The copula only connects nominal elements, but not nouns and verbs ("adjectives").
Don't forget that là is only one of the many possible copulas. Thì and có are better candidates in this case, but there's also bị, for example...
I am ill > tôi (bị) bệnh
it is red > nó (có) màu đỏ
you are tired > bạn (thì) mệt
that is a dog > đó là một con chó
In fact, "là" is the copula that is least likely to be omitted. :D
I just wrote this exact answer as the translation for "I am fine" immediately before this one, and was marked 'incorrect' saying I should have written Tôi khỏe.
They both mean the same thing, but it seems like theyre from different regions, different dialects. Its a bit confusing honestly