Some apps (for example, OpenOffice in some cases) don't provide _NET_WM_NAME(UTF8_STRING) and only provide WM_NAME(STRING) or WM_NAME(COMPOUND_TEXT). If such title contained Utf-8 characters, they looks like
'/'`'S'Q'q 'S'\']'Q'U'\'Q - Chromium
Новая вкладка - Chromium
. In some WMs (wmii for example) everything is displayed OK.
I've looked at wmii code and made a simple patch for JWM. It's maybe a bit ugly and is not using jxlib, but it works for me.
It uses XGetTextProperty and Xutf8TextPropertyToTextList instead of XGetWindowProperty.
PS: my locale is ru_RU.UTF-8, JWM-2.0.1