Ah, yeah, this is a little word that gets left out a lot in Welsh courses, and it can be omitted completely, yes.
I tend to use ‘ai’ in my natural speech, though, as many other people do, when there isn’t a verb in the sentence (apart from the verb ‘to be’, which is a funny kind of verb anyway, considering that ‘being’ and ‘doing’ are quite different, but that’s another thing!).
Ai Stella wyt ti?
Stella wyt ti?
Both mean: are you Stella? The ‘ai’ part is almost like another ‘is it?’ at the beginning. Is it Stella you are? Literally, - Is it Stella are you? but that’s just a horrible construction and Welsh people don’t think of it translated in that way.
The dictionary says that ‘ai’ is an ‘interrogative particle’. Some people in mid-Wales say ‘A ife’, or even just ‘ife’ instead of ‘ai’. (Said as ‘iv -eh’)
Ife Stella wyt ti? for example. I live in Ceredigion and this is heard quite often here.
The answer would be 'ie/nage (or simply just 'na) ’ in the South and 'ia/naci (or again, simply just ‘na’) in the North.
Personally, I think it would be easier for learners to know which yes and no to answer in Welsh if courses included the ‘ai’ part of such question because ‘ai’ questions would always be ‘ie/nage’ or ia/naci’… (not counting your ‘maybes’ etc). It’s quite hard, as you know, to get your head around the different ways of saying ‘yes’ in Welsh because apart from ‘ie/nage’, as seen above, the concept a one-word agreement (‘yes’) across tenses and subjects just doesn’t exist.
Oh, I think there are a lot more blog article ideas here!
Hope that helps @stella.