Just ask them directly. I've simply asked my Indian coworkers if anyone else in the workplace also speaks their native language and they have no problem talking

Just ask them directly. I've simply asked my Indian coworkers if anyone else in the workplace also speaks their native language and they have no problem talking about it. I've learned a lot from asking them about their languages. I've discovered that they generally share the same native language when they are from the same region in India, otherwise they don't. The only exception I've seen so far in Punjabi, since it seems that Delhi also has a significant population of Punjabi speakers who have migrated there from Punjab, which is farther to the west. Sometimes my coworkers do share languages, and that's obvious if I hear them speaking to each other in a language other than English. Sometimes they have to speak English to each other because that's their only common language.