Hi, we have already answered this in the beginning of the article: /wp-admin/css/ directory holds style definitions for the admin theme. You can manually edit each one of them to include new font faces (either local font file copies or from CDNs) and apply font-family changes throughout entire files where needed. However, we do not recommend this method at all, first, this is a very tedious job, and second you will lose option to auto-update WordPress for security and other improvements!

Can you suggest me, which file (in wordpress directory) is required edit to change the font face/family for wordpress admin theme, not for site

In order to change font on the front-end side, you need to either modify your theme or use a plugin that can change font/appearance of other themes, assuming that they are compatible (e.g. that theme supports font change through other plugins). There are many such plugins @ WordPress.org for front-end font customization (e.g. just search for “font”), so you have to try and test them and see which one works best. As far as I know, there is no universal single plugin that can change both admin and front side at once.

Regards

Thanks!

About support of EarlyAccess fonts, please read this support topic:
https://wordpress.org/support/topic/korean-username-shows/

Short answer, there are no plans to support them right now :(