have to force utf-8 encoding by lc_all when invoking X11 application from Vim command-line

[Konfekt]

Under OpenSUSE 15 with Awesome WM and Vim 8.1.0149 (as well as 8.0.1568), when passing parameters to a GUI-application, such as zeal or goldendict, utf-8 encoding is only used when set by LC_ALL, for exampleLC_ALL=en_US.utf-8.

That is, with the above environment variables, while :!zeal Jó shows J��, :!env LC_ALL = it_IT.utf-8 zeal Jó shows Jó. Same for other GUI applications such as goldendict.

Setting all other locale environment variables listed below, principally LANG, to use utf-8 has no effect.

LANG=it_IT.utf-8
LC_CTYPE=it_IT.utf-8
LC_NUMERIC="it_IT.utf-8"
LC_TIME=it_IT.UTF-8
LC_COLLATE=C
LC_MONETARY="it_IT.utf-8"
LC_MESSAGES=en_US.utf-8
LC_PAPER="it_IT.utf-8"
LC_NAME="it_IT.utf-8"
LC_ADDRESS="it_IT.utf-8"
LC_TELEPHONE="it_IT.utf-8"
LC_MEASUREMENT="it_IT.utf-8"
LC_IDENTIFICATION="it_IT.utf-8"

This does not occur when the GUI application is directly called from a terminal, such as urxvt or xterm, inside a shell, such as zsh or bash. It also does not occur when the program does not have a GUI, but runs in the terminal.