That's a good suggestion. There is no rule set as such. It's the zone that takes the call. Most of the times it is English,Hindi and the language of the state to which the train belongs, as you mentioned. But there are some examples which has both the languages of Source station and Destination Station. Best examples are : Bangalore - Chennai Shatabdi, Double Decker, Chennai - Mysore Shatabdi, Udyan Exp and many more. There are other instance where even passing by state's language is also used. Ex Yesvantpur - Mangalore Exp which has board in Kannada, Hindi, English, Tamil and Malayalam. There is one more example which has Source and intermediate state but not Destination state. Ex: Chennai - Mangalore Exp which has board in Hindi, English, Tamil and Malayalam. So there is no hard and fast rule, all depends on the Zone which own the train....