RTL layout detection got solved in Qt5.6, but one have to install the qt translations (that are not required right now). And therefore, the layout doesn't get mirrored. This is a problem in Arch, Ubuntu, and maybe all the other distros. Reproducible: Always
The problem is only on arch The problem is the package qttranslations5-l10n not installed automatically On Ubuntu the package qttranslations5-l10n installed automatically The problem on Ubuntu is Qt still on version 5.5, so you can wait for Kubuntu 16.10 or 17.04 (Or you can install the PPA Kubuntu Backports Landing, its have Qt5.6 and its work great, I testd this. but pay attention, its a test repo) I open bug too, about this problem on KDE Neon https://bugs.kde.org/show_bug.cgi?id=368050
It was fixed in Arch. https://bugs.archlinux.org/task/50780 I'm not sure about Ubuntu as it doesn't require the translations package: http://packages.ubuntu.com/yakkety/kde-l10n-ar No problems with Fedora.