Non-UTF8 encodings mess up some labels and texts

Although I picked the xfce4-panel as the culprit, the problem affects other components too: when the LANG is set to, for example, uk_UA.KOI8-U various labels and other textual entries get messed up badly.

Many, but not all. For example, the title of main application menu (called "Applications" in English), shows junk characters instead of Ukrainian "Програми" -- bad. However, in the popup menu itself, the entries are still listed in proper Cyrillic.

This seems like a 4.18 regression -- I still have 4.16 installed on a different machine, and everything looks good there. Changing LANG to uk_UA.UTF-8 fixes the problem, but I'd rather stick to the 8-bit encoding...

It feels related to the earlier bug 12294, but on a much greater scale 😞