On proxmox I was getting this error when connecting through SSH

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = (unset),
    LC_ALL = (unset),
    LANG = "en_US.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

Has to do with some locale that can't be loaded.

Fix:

Remove/Comment this line in /etc/ssh/sshd_config:

AcceptEnv LANG LC_*

Restart SSHD