It's not just population density - you need economic opportunities.
For instance, most large languages in India are dying off quite rapidly even in regions with high speaker density, since the Indian state and people prefer a discriminatory class system that privileges a foreign language. There are very few opportunities for non-English speakers, either educationally or economically. Normal speech has turned into a crass pidgin of English and the local vernacular; schooling has turned 'English-medium' entirely, thus creating a generation of idiots, fluent neither in English nor in their own native languages.
The Indian state being essentially the same as the colonial British Raj, will never tolerate empowering the natives of India, even if political cronies have and will continue to give it a sense of legitimacy by appealing to ethno-religio-linguistic rabble rousing.
As I understand it (and I hasten to say that I have no first-person exposure), there are at least a dozen official languages in India. One reason for the dominance of English is that speakers of languages other than Hindi resent what would otherwise be the dominance of Hindi. English is perceived as better because it's no one's first language, rather than the first language of a plurality.
For instance, most large languages in India are dying off quite rapidly even in regions with high speaker density, since the Indian state and people prefer a discriminatory class system that privileges a foreign language. There are very few opportunities for non-English speakers, either educationally or economically. Normal speech has turned into a crass pidgin of English and the local vernacular; schooling has turned 'English-medium' entirely, thus creating a generation of idiots, fluent neither in English nor in their own native languages.
The Indian state being essentially the same as the colonial British Raj, will never tolerate empowering the natives of India, even if political cronies have and will continue to give it a sense of legitimacy by appealing to ethno-religio-linguistic rabble rousing.
See, http://sankrant.org/2011/03/the-english-class-system-2/