How to Fix "bash: warning: setlocale: LC_ALL: cannot change locale (en_US)"

Tested on Debian.

Edit the default locale:

sudo vim /etc/default/locale

Add the following:

LANGUAGE=en_US.UTF-8
LANG=en_US.UTF-8
LC_ALL=en_US.UTF-8

Run these commands:

sudo locale-gen en_US.UTF-8
sudo dpkg-reconfigure locales

Note if you're connecting to a server the issue might be on either your machine or the server.