Most people who grew up in New Zealand (including myself) will have learned Maori, which I would say fits your criteria, at some point, but most not to any degree of proficiency.
A few years ago I spent quite a bit of time in south India and started learning Kannada, the native language of Karnataka state, but I have no idea how many Kannada speakers there are (off to check Wikipedia....) Oops, it doesn't come anywhere near qualifying, it has 38 million speakers. I should have known, it being an Indian language. I bet not that many people outside India have even heard of it though.

