Why does perl crash: warning: Setting locale failed?

Question

Perl

Every day on my Debian server the same error occurs:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
  LANGUAGE = (unset),
  LC_ALL = (unset),
  LC_CTYPE = "UTF-8",
  LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I do:

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

It is treated, and the next day again

Answer 1

apt-get install locales
dpkg-reconfigure locales

add en_US.UTF-8
then select it by default in the system environment