Created attachment 110215 [details] screenshot-1 All Qt/KDE applications don't want draw cyrillic Terminus-12, instead of GTK+ such as Emacs and Leafpad. Cyrillic Terminus-14 and greater works well. And that situation occurs on all my KDE NEON computers. On other distros like Gentoo and Arch KDE applications work well. P.S. Sorry, I know that's wrong place for this bug, but i simply don't know what kind of bug it is.
Font fallback is decided by Qt. Please report this issue directly to Qt developers via https://bugreports.qt.io/