Regarding the language support on login
The instructions do no always work (https://bbs.archlinux.org/viewtopic.php?id=196248 and I got this too) but there is a work-around
"Alternatively, if the above doesn't work for some reason, you could edit the file /usr/share/sddm/scripts/Xsetup and add the command setxkbmap -layout ISO, e.g. setxkbmap -layout se for a Swedish keyboard." I don't know if you want this included or if we are doing something stupid to not getting it to work. --Shieldfire (talk) 08:46, 1 June 2015 (UTC)
Regarding SDDM and root login
There is some discussion on root login in SDDM here: https://forum.kde.org/viewtopic.php?f=289&t=124502&hilit=dolphin+plasma+5#p328070 Don't know if it's a "feature" or something is broken in SDDM or if it's a bug in Arch (and openSuse).