The other day, I happened to be on the platform of JR Kichijoji Station as a Sobu Line express pulled in. Wanting to be certain it would stop at the next station, Nishi-Ogikubo, I inquired to the young man standing next to me. In halting Japanese, he said that he was Chinese and didn't understand my question.
The train doors had already opened, and lacking time to accost a native, I repeated my question in Chinese, which I must credit myself with having the foresight to learn many years ago -- for use someday at encounters just like this one. The man was momentarily taken aback, but knew the answer. We boarded the train together and, after exchanging a few pleasantries, I bade him a pleasant farewell and disembarked at Nishi-Ogikubo.
Actually these sorts of encounters have been happening to me with some regularity. I might be seated on a train and notice that the passenger beside me is reading a Chinese magazine. Or perhaps overhear one having a conversation in Mandarin.