Update: Google India today clarified that Hindi support for the Assistant has not been launched and Hindi support is only available in the Google Assistant as part of Allo. Check out the official statement below.
The Google Assistant on Android phones and iPhones is currently available in English in India, built for English input but supporting a few selected Hindi queries. While we’ve launched the Hindi Google Assistant on Allo, it’s not available on phones yet. We are looking to bring the Assistant experience to more Indian languages over time.