How cohesive is India as a country?

Hello everyone, I'm ethnically Chinese, but I've lived in Canada my whole life. As a person who's studied a lot of Chinese history and politics, I recognize a lot of similarities between China and India, at least on a surface level. Both countries have incredible diverse and massive populations (1.4b). They also have a big landmass, and are developing their respective economies. Both suffered at the hands of European colonizers, but India more than China due to its total subjugation by the British, while China was semi-colonized like Persia and the late-Ottoman empire. My question is does everyone from south to north (majority not fringe) see themselves as Indian? How is this identity maintained despite the lack of a common language? Is it through Hinduism? Mandarin also wasn't commonly spoken everywhere in China until relatively recently (thus the similarities), but the Han Chinese had a long history and tradition of being ruled centrally by one polity. The experiences of the 20th century also helped forge and reinforce the Chinese national identity. Provincial and regional identities still run deep in China, but most people are fairly patriotic/nationalistic, though some lament the loss of their local language. There are also complaints about tax dollars of wealthy region being sent to poorer inland provinces and to help the sarcastically named "African brothers" (Belt and Road).