Coming from here ( french ) Comment installer KDENLIVE avec 20.04 ? / Questions et informations avant l'installation / Forum Ubuntu-fr.org I was trying to help.
So the idea is to install latest version of Kdenlive from its stable ppa.
Like the op I end up with something whilst usable, incomplete : Kdenlive is not in my language ( very annoying ) and not themed accordingly to my settings ( Qt5 style not applied, this is less annoying ).
Installing language-pack-kde-fr did not help for language.
Installing adapta-kde-theme ( which brought also kvantum ) did not help either for theming.
Abelthorne suggests it might be related to absence of
~/.config/Trolltech.conf file ?
I know it’s not Gtk - so I don’t expect a 100% match but not having such a heavy software in user’s language is a no go. And well I don’t have those problems in scribus which reads french and is 99% correctly themed ( following my customization in Qt5 settings ).
So what’s to look at ?