If KDE screen is locked with CJK input system active, password input is no longer possible, since there is no way to change the input method (default keyboard shortcut would be ctrl + space) from a locked screen. Hence a password named "password" would then become "ぱっすぉrd". And since these two strings obviously do jot match, login is no longer possible. ubuntu 14.04 LTS
cf. https://bugs.launchpad.net/ubuntu/+source/qt4-x11/+bug/1413159
I'm sorry about your bad experience. Unfortunately 14.04 ships with a Plasma version no longer maintained. For this specific problem we have a workaround in Plasma 5. See bug #306932