Ctrl+Shift+u does not work on Kubuntu 18.04

I have installed Kubuntu 18.04 and want to input unicode characters, but Ctrl+Shift+u combo does not work. I also try to install ibus using sudo apt install ibus ibus-gtk ibus-qt4 ibus m17n, then call ibus-setup, but this combo key does not work now although it works on Kubuntu 16.04.

when I attempt to change input method to "other unicode(m17n)", it fails and gives

(ibus-daemon:1738): GLib-CRITICAL **: 23:13:26.272: g_variant_unref: assertion 'value != NULL' failed

How I can input unicode on Kubuntu 18.04 by any other Methods?