Locale not supported by C library - Virtual Desktop in Redhat 7.7

I am running a Redhat 7.7 server with REALVNC. The service mode is running fine.

In the virtual desktop mode, the gnome terminal is not starting. If I try „gnome-terminal“ in a xterm window, I get the following error message:

# Locale not supported by C library.
#       Using the fallback 'C' locale.
# Error constructing proxy for org.gnome.Terminal:/org/gnome/Terminal/Factory0: Error calling StartServiceByName for org.gnome.Terminal: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.gnome.Terminal exited with status 9

I have checked the gnome wiki under https://wiki.gnome.org/Apps/Terminal/FAQ#Exit_status_9, but I do not understand the reason (citation):

"Reason: The locale settings in the environment that gnome-terminal-server is started with describe a nonexistent locale. Consult your distribution's documentation on how to fix this. Note that is it not relevant to check the locale settings from a different terminal (e.g. xterm); what counts is the environment that the systemd --user instance passes to the processes it starts."

As I said, the Redhat machine itself and the service mode work fine. The virtual desktop does not work.

Can you give me a hint to solve this issue?