Description:
Since a recent (full system) update, both SDDM and the KDE Plasma session I launch with it use a US keyboard layout.
When in KDE, the chosen layout (de-neo) is ignored, while SDDM only shows US layout in the selection.
I assume this is related to the fact that X runs as root again (IIRC it didn't before the update), even if I start KDE using GDM (which respects my layout) instead of SDDM.
Since pacman AFAIK cannot show me a list of recently updated packages (I just filed a feature request for that: https://bugs.archlinux.org/task/51134), I am kind of in the dark with finding out which package caused the breakage.
I did however check xorg-server, sddm and systemd (I assume systemd-logind, which IIRC is used for non-root-X, resides here), but none of them was updated in the last few days.

If you have any idea which other package could have broken the system (I don't know which ones from KDE may be relevant), I would be glad to check.


Steps to reproduce:
Select a non-US keyboard layout in KDE.
Enable SDDM.
Start system.
Select your user with non-US layout.
Check selection of keyboard layouts (should default to the user's preference and potentially have other alternatives, but only shows US layout here).
Login to “Plasma” (X11) session.
Open some program that has a text field (the KDE start menu (Alt-F1) or krunner (Alt-Space) for instance) and type (should show text according to the user's preferred layout, but uses US layout on my system).