This is a question I have encountered several times during my time in the US. Most of the time I get by saying I don’t. But, in some cases I try to tell them the linguistic diversity in India and how there is not, and there probably will never be a unified language called Indian.
But, when I try to explain this, I always had only anecdotal evidence, telling that the states are divided by major languages and then there are several minor languages, which, are not dialects of the same language etc.
Today, I found this very interesting visualization that shows the linguistic diversity of countries. The chart is here http://manyeyes.alphaworks.ibm.com/manyeyes/visualizations/linguistic-diversity-by-country
The darker the country’s color is, more linguistically diverse it is. The nominal value of the index is the probability of two random people in the same country speaking two different language.
The website Many Eyes is a wonderful place for collaborative data visualization. I can see myself playing around with the wealth of data and very creative visualization tools.