Many languages are spoken in Mangalore, Kannad and Tulu are main. However, I think Hindi will also do because generally, Hindi is also common in Karnataka and there people are not very rigid about their language like some other states. That brings the question, why CVs chose Mangalore for Ganga's college? It could well be within Rajasthan/North India.
Mangalore is a hub for medical and engineering education. Infact it is Manipal which is closeby.
Just like mumbai.
Mangalore, Mumbai, Delhi and Vellore are more famous and well known. They must have chosen Mangalore so that ganga will be far away from Jetsar for a while and also safe from ratan's henchmen.
I have stayed in Mangalore for some years and the main languages are Kannnada, tulu and konkani as well as malayalam as it touches Kerala. It is not like bangalore or Hyderabad where hindi is understood easily as even muslims of mangalore dont speak much urdu.