For people running into this and not knowing how to easily fix:
Feb 20 09:15:19 tequila sshd[18110]: pam_env(sshd:setcred): Unable to open env file: /etc/default/locale: No such file or directory
tequila:~# ls /etc/default/locale
ls: cannot access /etc/default/locale: No such file or directory
tequila:~# update-locale
tequila:~# ls /etc/default/locale
/etc/default/locale
Or just fill it yourself:
tequila:~# cat /etc/default/locale
# File generated by update-locale
LANG=en_US