In Thor: Ragnarok Hulk has taken full control, Banner states that usually, he feels like he's got a hand on the wheel but this time he had no awareness of what was happening. So Hulk did seem to become stronger mentally and take fuller control. This leads to Hulk talking.
Before that, we never saw Hulk talking, until Avengers: Endgame Banner again tests with Gamma radiation and end up becoming Professor Hulk.
But in Endgame when the heroes traveled back in time to get the Infinity Stones, at the events of The Avengers (2012), we see that Hulk from that time period talking. Which was never shown in the The Avengers (2012).
So is Hulk able to speak all the time and did he hide this from other Avengers?