The 27-year-old, who reprises her "Iron Man 2" character Natasha Romanoff, aka Black Widow, in the blockbuster, learnt her superhero's native tongue for some key scenes.
"I had two days, so I had to learn it phonetically.
I knew what I was saying but I had to be able to pronounce it and breathe some life into the lines so that it didn't sound like I was repeating some Berlitz (language learning) tape.
"We hired this great Russian translator, and she worked with the dialogue coach. She was really expressive, which helped, so my mouth found the words in a way that didn't just sound like I was a parrot," Johansson said.