What is the best practice when translating a site to Chinese, go with URLs in Chinese or English?
Could you please share the reason why?
The URLs should be in the same language as the content. Ideally you would also translate the relevant path segments (like "product" in your example), not only the slug.
A URL that’s in a language users might not understand is useless for them. A good URL is descriptive, it gives an idea what the content is about. If it’s in a language the users don’t understand, they can’t get this idea. And they might not be able to type it (e.g., in case it’s printed / written down), they might not be able to dictate it (e.g., via phone), they might not be able to recognize it again (e.g., in case they try to remember if they already visited it), etc.
It could even stop users from visiting the page, because they might assume that the page’s content will also be in this language. Language codes in the URL could help here, but not all users might recognize them.