INDIA, April 16, 2018 (Quora, by Ram Abloh): Sanskrit was the spoken language of ancient India, in spite of what the modern miscreants would like you to be indoctrinated with. The feature that distinguishes a spoken language from a purely literary or artificially constructed language is that the former quickly develops variants, whereas the latter is frozen forever. All other great languages in the history of the world have had variants - such as accents (variants in pronunciation), lexicons (variants in choice of vocabulary), registers (variants in style based on purpose or social setting), and dialects (variants that are geographical with a combination of one or more of accent, lexicon and register). English, for example, has 28 variants just within England! (not including Scotland, Ireland, Wales, North America and Australia). Now, English was born around the 7th century AD, so it has been active for about 1400 years.
Sanskrit has been around since at least 3000 BC (based on astronomical evidence in Vedic & post-Vedic literature), so it was the de facto language of a vast portion of the Indian subcontinent. It was actively spoken well into the early centuries AD. So it has been active for at least 3500 years. Also, India is about 30 times the size of England. So I don't think it is unreasonable to allow for a few regional variants to sprout up through 3500 years and a vast landmass.
Evidence for Sanskrit having been a spoken language is abundant. There are hundreds of everyday words in the Vedas that do not serve any religious purpose. Similes and metaphors use everyday words. If Sanskrit was not a commonly spoken language but only a strictly liturgical language, such everyday words would not exist, as they would not serve any religious function. So you see, a great living tradition such as the Vedic culture cannot have thrived if Sanskrit was a sterile language that was only used by "priests in temples." Sanskrit was the language of the streets and the elites, of traders and philosophers, of prostitutes and saints, of farmers and kings, of housewives and warriors.
Much more of this discussion at "source" above.