Buttons for setting language priority (up, down, remove) cannot be clicked on. Thus you cant change your language preferences. Problem ocurs since language settings redisgn in Plasma 5.12.90.
in plasma 5.13.80 (up to date neon-devedition-gitunstable) the button actions works for me
(In reply to Burkhard Lueck from comment #1) > in plasma 5.13.80 (up to date neon-devedition-gitunstable) the button > actions works for me I use Arch with KDE_unstable repo and I just hope it will get fixed until Plasma 5.13 stable is released.
Fixed in Plasma 5.13