The 29-year-old actor stars alongside Dame Helen Mirren in Woman In Gold, which tells the true story of Jewish refugee Maria Altmann and her legal battle to reclaim from the Austrian government five paintings by Gustav Klimt stolen by the Nazis during World War II.
Max appears as Maria’s husband Fritz in the flashback scenes, which show her meeting and marrying him, and their flight from the Nazis.
He admitted learning German took “a fair bit of practice” but he didn’t feel he had much choice.
Max explained: “It was a funny day because when I got told about this part, the producer, Harvey Weinstein, said to me ‘We’ve got this part we want you to play, do you speak German?’
“And I said, no I don’t and he said, ‘Well can you learn it by tomorrow and get to this audition?’
“Which was terrifying – and for any other person I might have said that’s unreasonable, I can’t do that, but for him you just suck it up and do it.
“And that somehow got me the part, and then they got me an Austrian voice coach and we worked every day so by the time they actually got to the day of shooting it, it was so embedded in the back of my mind it was fairly straightforward.
He added: “It was the singing, the opera singing that was a complete nightmare.”
In the wedding scene in the film, Max has to perform an operatic song. He revealed: “The training was lots of standing in a room looking in the mirror singing at yourself, hating yourself.
“On the day [the director] Simon Curtis said, ‘Right everyone in!’ And I said, just give me five minutes to do it by myself, can’t I just do it once by myself? And he said, ‘No, that’s how you get scared.’
“He was wrong, his way was far scarier, he filled the room and made me do it a capella. But once that was out of the way, it actually became quite fun, and by the end of the day I didn’t want it to stop.”
Max hasn’t kept up his opera singing.
“Definitely not! I sing in the shower, and that’s about it,” he laughed.
Although The Riot Club actor shares no scenes with Dame Helen, he was very nervous about meeting the Hollywood royalty on set.
He revealed: “We spent a little bit of time in the make-up trailer. I was terrified I was meeting the Queen. Everyone calls her Dame Helen and I was so scared, I made sure I got the heads up the first time I saw her, and prepared myself, and I was practically curtseying.
“But then I met her and she was lovely and self-deprecating and witty and gentle and great.”
Woman In Gold, which also stars Ryan Reynolds and Katie Holmes, opens in cinemas on Friday April 10, 2015.