If its the part where he's revealed to be Reeve, then there is a reason for the accent change because in the Japanese script Reeve speaks with one type of dialect while Cait Sith speaks in another, but when he gets razzeled by the events with the Sister Ray and Rufus' death, he accidentally switches the accents (hence the comment Heidegger and Scarlet make) which reveals to Cloud and company of Cait Sith's identity.

Granted, it's still a shoddy translation since Cait Sith's speech was barely given any accent through most of the game, but that's still most likely why that scene is a bit weird.