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.
Remove/Comment this line in /etc/ssh/sshd_config:
AcceptEnv LANG LC_*