How to fix perl: warning: Setting locale failed in APT

First, check which locales are currently available on your system:

locale -a

This shows all installed and generated locales. If en_US.UTF-8 is missing, you need to generate it.

On Debian and Ubuntu systems, use the locale-gen command to generate the locale you need:

sudo locale-gen en_US.UTF-8

This creates the en_US.UTF-8 locale. You can replace en_US.UTF-8 with your desired locale (e.g., de_DE.UTF-8, fr_FR.UTF-8).

After generating the locale, update your system-wide locale settings:

sudo update-locale LANG=en_US.UTF-8

This modifies /etc/default/locale and sets en_US.UTF-8 as the default locale for all users.

Check that your locale settings are now correct by running:

locale

This displays all locale environment variables. Confirm that LANG is set to your desired locale:

LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
...

Alternatively, you can use the interactive dpkg-reconfigure command, which is often easier:

sudo dpkg-reconfigure locales

This opens a menu where you can:
1. Select which locales to generate (use arrow keys and spacebar)
2. Choose which locale becomes the default
3. Confirm your selection

Select at least one locale (e.g., en_US.UTF-8) and choose it as the default in the next step.

If you cannot use sudo, you can temporarily suppress the warning by setting LC_ALL in your current session:

export LC_ALL=C.UTF-8

Or set it to your available locale:

export LC_ALL=C

This prevents Perl from attempting to use unavailable locales. To make this permanent, add the export line to your ~/.bashrc or ~/.zshrc file.