I was not sure to start PR as I thought the problem is unique for my setup, but recently I found similar problem on FreeBSD forum. The problem is then KDE translation changed, any KDE update breaks text rendering on various KDE components. For example, here is simple test. 1.Go to KDE settings -> Locale parameters and set it to russian (ru_RU). 2. Logout-Login. Start terminal and check locale output. Strange thing it won't be UTF-8 russian. 3. Repeat step 1 and step 2. It will be UTF-8 russian. 4. Log out. 5. Delete ~/.cache and log in. 6. Now font rendering is broken. For example, KDE settings misses all descriptions. 6.1. If you have avatar, it disappears from locking screen (but not from sddm screen). 7. Workaround: log off, delete ~/.cache , delete ~/.config/plasma-locale-settings.sh and ~/.config/plasma-localerc, set desired locale. 7.1. Not sure how to bring avatar back though. I have this issue after every (even minor) KDE update on all computers I run FreeBSD/KDE. Hope, this one is not unique.
I have the same problems with font rendering in ru_RU.UTF-8 locale. For myself, I found a solution and described it here https://bugs.kde.org/show_bug.cgi?id=399143#c27. Problem with avatar due to OpenGL, I think. If you use the card and driver nvidia, then there is no problem. For my project ulbsd.ru, I rewrote the screen locker code without using OpenGL. And the avatar is displayed normally.
Thanks! This solution works. As this is the issue with KDE itself, probably we can close this one.