I only learned about it when somebody pointed it out to me in an HN thread a couple of years ago, like the parent. The button is small and I think since I don't speak Chinese or Japanese my brain tends to skip Chinese characters as I assume that whatever they convey is not aimed at me. It's also alone on the left-hand side, with no decoration or styling showing that it's interactive.

A flag icon or simply some more explicit text would be vastly easier to understand for me, especially if it actually looked like an interactive element.