I watched Supernatural in Latin-dub, because Spanish is my first language– and I have to say I had high expectations for Castiel's confession and Dean saying 'Y yo a ti, Cas'... but LOL.
It feels out of place. It doesn't sound like Dean, I swear– I'd rather stick with Dean's original response and believe that he just couldn't get the words out because he was too shocked and overwhelmed by Castiel's words... it's more painful but more significant and more Dean.