How many sites do this but you don't notice because they default to English?
However, the right solution is still to use the language header. I send that to them, they should use it to give me the right one by default.
One of the funny things is that this whole site is in an iframe; which breaks both Google Translate, and the Firefox translate feature. If you check, the outer iframe seems to indicate `lang="en'` and loads the iframe with `src="/coder/index.html?lang=en"`, but the inner iframe still gets a `lang="zh-CN'` by default until you use the toggle.
If you go to the eventual redirect source of the page with `lang=en` parameter, you get a `lang="en"` attribute, but it's still in Chinese until you toggle it with the menu: https://mimo.xiaomi.com/coder?lang=en
Anyhow, yeah, lots of pages are probably broken this way but we don't notice. But still, it has that info from your request, it should use it.