Q: If I correctly identify and spell the name of the face-down side of another player’s card, am I required to confirm it to the center row? 

A: No. You are required to leave it on the new face-up side, but confirming it to the center is optional (with that player’s permission) and does not use up an action.

Q: Do I really have to spell the name of the card out loud and spell it correctly to get the bonus of leaving it face up and confirming it? 

A: Yes.