A 404 error occurs when refreshing an app using next-i18next

I'm making a multilingual service using next-i18next, but there seems to be an error related to routing

Git Repository: https://github.com/fatherslable/test-repo

problem situation

1. If you connect to localhost:3000 and press refresh, there is no problem.
2. There is no problem even if you connect to localhost:3000/test and press refresh.
3. If you connect to localhost:3000/en and press refresh, there is no problem.
4. If you connect to localhost:3000/en/test and press refresh, a 404 error occurs.

It seems that my next app cannot find the page if I refresh it while the language of another country such as en is applied instead of ko.

What am I missing?