interestingly found an article in today's TOI on "Talking Native"
" In a country where state boundaries have been drawn on a linguistic basis, it is no surprise that language regularly emerges as a bone of contention..."
"India, which has 22 scheduled languages (the number increased from 18, when Bodo, Dogri, Maithili and Santhali were added to the list in 2003), has also seen some shift in the language profile of populations. In the 1961 Census of India, 1,652 mother tongues were recorded. However, the 2001 census listed only 234 identifiable mother tongues — those which have 10,000 or more speakers each at an all-India level. "
'Hundreds of languages are in a similar state the world over. Reports from Unesco say over 50% of some 6,700 languages spoken today are in danger of disappearing. Experts estimate that 96% of the world’s languages are spoken by 4% of the population, and one language disappears on average every two weeks. "
some very interesting information about indian languages here
Though couldn't find much on how the states were so formed based on linguistic differences..