I'm not the best person to answer this but one of the problems with direct translation with the Obama phrase is that there isn't really a word in Irish for "yes". Sea is just 'Is ea' as far as I'm aware. "Sea, is feidir linn" doesn't sound right to me. As a result "is feidir linn" really just means "we can" but in Irish you answer questions with the verb and not a word so its fine to just use that.