The 48-year-old has been taking lessons over the last four months as his character in the movie demands fluency in the language.
"Aamir has been trying to master Bhojpuri for the last four months. Everyone is wondering why he has been learning a language that is traditionally spoken in east Uttar Pradesh and Bihar, when the film has largely been shot in Rajasthan. This is a new twist to the tale. There is a lot of curiosity as to what the film is about," a source said.
This is not the first time the 3 Idiots star has taken language lessons for a role. He learnt Awadhi while preparing for Ashutosh Gowariker's blockbuster Lagaan. Peekay, which also stars Anushka Sharma in the lead, is expected to release next year.