I don't know if this is true but based on his past games, I can see that Pacquiao don't let his opponents get in his head, he let his fist talk.
There are a lot of times that his opponent trash talk him, some might defeated him, some are knocked out but I don't heard or seen him trash talking his opponents. Yes there are times that he say the ending of the game like he can end the game in round 7 or such. I don't see this as a trash talk but just an analysis when to end or what round will the fight ends.