can I say

Your original premise is wrong. English speakers say both "You could say . . . " and they say "You can say . . . " Therefore, the same cases apply in the first person singular. I would go on to point out that the conditional is very less likely to be used than the present Indicative form, as an interrogative.

To Set's reply I would only add that to me, these phrases above are not exactly synonymous, and so not interchangeable in all cases.
(but they are very similar)

Thank you.

Hi WBYeats<
I think both are correct if used according to the situation.