Thank you @vinothkannans
There are two questions about the directory when selecting ascii in the slug generation method.
One thing is about not displaying any content on .../t/. Is it possible to display a list of topics here?
The second is about displaying randomly selected topic page when opening .../t/topic/. Is it possible to display a list of topics here?
(Also, I do not know why ../t/topic/ is generated again in the hierarchy below .../t/.