Finding the voice of a character - especially when there's an accent or regional dialect involved - can be a particular challenge for certain actors.
There's the fear of overselling it, underselling it, how the accent plays with dialogue, but once you've got locked in, it can sometimes be hard to drop it. In other cases, it's better just to keep it going through the shoot - and that's pretty much what James Franco did.
According to an interview with Jason Mantzoukas in EW, James Franco apparently directed The Disaster Artist using Tommy Wiseau's voice and speech pattern. "Franco directed the whole movie in character as Tommy Wiseau. Well, I should amend that - he wasn’t in character as Tommy Wiseau, but once he started the day doing Tommy’s voice, he would spend the rest of the day doing the voice. So, it wasn’t like he was pretending to be Tommy, but it was like James using Tommy’s speech pattern and accent."
Mantzoukas, who currently stars alongside Will Ferrell and Amy Poehler in The House, has a small role in The Disaster Artist as a camera salesman. The scene, which is lifted straight from Greg Sestero's behind-the-scenes biography, involved Wiseau not understanding the difference between 35mm and video - or renting as opposed to buying cameras. "Hannibal Buress and I play the people that run the rental house. There’s this great scene where Tommy is insisting both on the fact that he wants to shoot it on digital and 35mm concurrently, and that he wants to buy all of the equipment, not rent it. So, it’s this very funny scene of confusion and miscommunication between the four of them."
There's still no word yet on an exact Irish release date for The Disaster Artist, however it's been confirmed that A24 is expected to give the film a wide release so there's every chance it'll eventually screen in Ireland in the future.