It might be related to translations. When you use zh-cn, we have a translation for that language, so you're redirected to it. Not sure why you get a 404 though.

Le 26 février 2021 21:18:12 GMT-05:00, ylc991 <ylc991@163.com> a écrit :
Hello! My webbrowser has set ‘Accept-Language’ to 'zh-CN,zh' by default, and https://guix.gnu.org returns 404. I have tested with curl, 'zh-CN,zh', 'zh-CN', 'zh-cn' is 404 while 'zh', 'zh_CN' is 200.

The first time I found it is on 2021-02-23. And it didn't happened about one or two months ago. I think there may be something wrong with the web server.