Last week i was trying to make my Raspberry Pi work again, and while reinstalling and upgrading Raspbian OS packages i run into an issue where a perl warning is displayed.

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The warning message apprears during the installation packages(invoking Perl) and it's due to missing locales being set not :

[...]
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LC_TIME = "fr_FR.UTF-8",
        LC_MONETARY = "fr_FR.UTF-8",
        LC_ADDRESS = "fr_FR.UTF-8",
        LC_TELEPHONE = "fr_FR.UTF-8",
        LC_NAME = "fr_FR.UTF-8",
        LC_MEASUREMENT = "fr_FR.UTF-8",
        LC_IDENTIFICATION = "fr_FR.UTF-8",
        LC_NUMERIC = "fr_FR.UTF-8",
        LC_PAPER = "fr_FR.UTF-8",
        LANG = "en_GB.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
locale: Cannot set LC_ALL to default locale: No such file or directory

Solution

You can fix the issue by setting the locale to en_US.UTF-8 for example:

$ export LANGUAGE=en_US.UTF-8
$ export LANG=en_US.UTF-8
$ export LC_ALL=en_US.UTF-8
$ locale-gen en_US.UTF-8
$ dpkg-reconfigure locales

Once you run the last command a dialog will appear to let you choose the desired locale.