Comment 3 for bug 1334495

I experimented a bit more yesterday. I didn't find a option for the sub-locales in KDE, but installed language-selector-gnome, where it is possible to change.

To be on the safe side, I just also directly edited /etc/default/locale as suggested by you.

After reboot:

"cat /etc/default/locale
LANG="de_DE.UTF-8""

"locale
LANG=de_DE.UTF-8
LANGUAGE=de:en:zh:en
LC_CTYPE="de_DE.UTF-8"
LC_NUMERIC=de_DE.UTF-8
LC_TIME=de_DE.UTF-8
LC_COLLATE="de_DE.UTF-8"
LC_MONETARY=de_DE.UTF-8
LC_MESSAGES="de_DE.UTF-8"
LC_PAPER=de_DE.UTF-8
LC_NAME=de_DE.UTF-8
LC_ADDRESS=de_DE.UTF-8
LC_TELEPHONE=de_DE.UTF-8
LC_MEASUREMENT=de_DE.UTF-8
LC_IDENTIFICATION=de_DE.UTF-8
LC_ALL="

The problem still exists.

Additionally I tried some more programmes. My impression now is that the problem only exists with KDE, e.g. QT programmes and things like all window titles. In Gnome applications (I tried Geany and Pidgin) Chinese text is displayed normally, in Thunderbird too (not sure what toolkit thunderbird uses).

I deinstalled "fonts-arphic-ukai" which seemed to be the "italic" font used. Now, text is still displayed using two different fonts, but the "italic" font changed. (I am using "italic" and "normal" to describe how the fonts look, but it is not equal to a text's attribute in Latin script. The difference between the two fonts could perhaps be compared to serif and sans serif in Latin script)

In the font settings, everything is set to Ubuntu, except for the monospace font which is set to Monospace.