[Решено] Root URL redirect doesn't work

Background of the issue:
I am trying to specify a root URL that redirects to a default language. The issue can be seen at скрытая ссылка.

Symptoms:
Instead of redirecting to the specified URL under `HTML file`, I got a white page.

Questions:
Why is the root URL not redirecting to the default language?
How can I fix the white page issue?