Does GRAV support utf8 folder name?

I guess does not...
nor utf-8 alias

What kind of folder name are you trying?

I tried and Grav didn't seem to work with the folder names which had UTF-8 characters for example "hùng-trần" (my name), I got 404 when access those pages. It is ok in my language, we don't often use UTF-8 characters in URL, in the given example we can convert the folder name to "hung-tran" instead, but I'm not sure about other languages like Arabic or Hebrew.

Mmm works for me, I am trying on OSX.
So it's not a grav-specific issue probably.

Could it depend on the type of file system used?

I use Debian. Maybe it is a problem with the way data is stored? Admin plugin only supports alphanumeric characters for folder name so it is not possible to change folder name via admin panel, I need to use file manager or FTP client to edit.

I tried to rename a folder name to Hebrew word by copy-paste (I can't type Hebrew) and I got 404 error.