Reply To: Lost passowrd page conflicts with Woocommerce Theme and Chinese username issues
I am not going to lie but this chinese username thing is tough to find a fix for since I think most of the work does need to be done for WordPress itself.
You can try going here and posting a topic aobut this issue to see if anyone has a good suggestion/workaround.
https://zh-cn.forums.wordpress.org/
Other than that I guess you might want to look in users keeping english characters in their usernames. I even found a bbPress chinese forum in the wild and they all seem to just be using english characters for their usernames some even numbers which is interesting, because using the users id instead of their username will definitely help you.
cos.name/cn
The forums topics using the id looks like they might be using this.
https://wordpress.org/plugins/bbpress-permalinks-with-id/
But since you seem to be getting the users to at least register with the characters now. Do you know what each user profile url is in the topic/reply post. Can you check it out in your browsers dev tools so I can see what the url is. I am expecting a url with some chinese characters and maybe some of these %%% in the url which would be leading to a 404.
