Hi,

I use multiple Linux distros, namely openSUSE Leap 42.2 and Debian Testing, both with KDE desktop. The versions are the following:
KDE Plasma version: 5.8.3 (openSUSE), 5.8.4 (Debian)
KDE Frameworks version: 5.26.0 (openSUSE), 5.28.0 (Debian)
Qt version: 5.6.1 (openSUSE), 5.7.1 (Debian)

Some KDE applications (e.g. okular, krename, etc.) still use KDE Development Platform 4.14. The GUI of these applications is drawn using a different font than the GUI of those which use the new KDE Frameworks 5 (Noto Sans 10). See the two images below for a comparison (okular [KDE Dev Platform 4] vs dragonplayer [KF5] on openSUSE, however, fonts are different on Debian, too).



The default font in both (Plasma 5) System Settings / Fonts and Qt 4 Settings is set to Noto Sans 10.

Please help me changing the UI font of applications still using KDE Development Platform 4, so that Noto Sans 10 is used everywhere. I have been searching for the appropriate config file in vain.

Thank you very much in advance!

A solution for openSUSE has been found here:
https://forums.opensuse.org/showthread.php/522507-KDE-fix-fonts-in-applications-using-KDE-Development-Platform-4-14-%28e-g-okular%29?p=2810576#post2810576

[...] I installed kdebase4-workspace-addons package which provides /usr/bin/systemsettings. It does not conflict with its counterpart from KDE5, because in kde5 the executable is called systemsettings5. Anyway, I executed this newly installed systemsettings and it miraculously synchronized setting for KDE4 apps with those from KDE5.

Note that synchronization was not miraculous in my case, I had to set the font manually. I still haven't found any solution for Debian stretch, though (a package with the above name does not exist, and package systemsettings already contains systemsettings5).