Progress buttons go out of the screen in the VirtualBox (800x600 fixed screen size), when one of CJK languages is selected

This problem occurs from the installation of the Ubuntu 20.04.3 LTS image, and if one of CJK languages is selected.
(maybe it also seems occuring from the Ubuntu 21.04)

I was about to try go to the "Next" after each doing selection of installation property.
but < Back, Next > and Cancel buttons are out of the screen, so every user cannot select by mouse,
just some of expert user can guess each button's position by pressing "Tab" key.
there is wide space internally in the installation window,
it's like that .. Its spaces should be shrinked.

I am teaching the way of handling linux shell terminal to many students.
I currently recommend to install this into virtual machine created by the Oracle VirtualBox to many student for getting experience of using linux terminal.
usually, screen size of VirtualBox machine is fixed to 800x600, and it cannot be varied by a user until VirtualBox guest driver is successfully installed into the Ubuntu machine.
Many students are suffered from this bug. so they cannot try to use this distribution.
they are demending why buggy Ubuntu distribution is recommended.

This bug should be handled as "urgent", please consider to make quick fix for this bug.
Thank you.