The decision was taken after intense discussions between director Aanand L.Rai of "Tanu Weds Manu" and Sonam.
As per the script, Dhanush plays a local Varanasi boy, and Sonam essays a Varanasi girl educated in Delhi.
Sonam will now spend time on the JNU campus to grasp the conduct and ideology of students there.
"The culture of education at the JNU is radically different from other universities in Delhi and across the country. At JNU students, both male and female, are very politically aware," said a source from team of "Raanjhanaa".
"They talk intelligently on national issues. They dress sensibly, hang out at specific cafes in Delhi, attend seminars and protest actively on national issues. The director Aanand Kumar wanted Sonam to imbibe all of these traits. And they also speak fluent Hindi," the source added.
When it comes to her spoken Hindi, Sonam, according to the source, needs to work as hard as Dhanush.
Dhanush is in Mumbai working on the dubbing of the Hindi version of his wife’s film "3". He has been working with a Hindi coach, trying to get the language right.
For Sonam too, it’s been decided that her accented Hindi and the haute-couture look just won’t do for the film.
However, Sonam does not really play the quintessential Varanasi girl. Her character is that of a local girl who has been to college in Delhi for three years, and returned to her home town as quite the sophisticated small-towner with an acquired metropolitan air, says a source close to the project.
At first the director was not sure if Sonam could carry off the role. But after meeting her, he was convinced.
"I am bowled over by her commitment to get the nuances of the role right. I’ve found my lady," said Rai.