perl: warning: Falling back to the standard locale ("C").

Если perl выдаёт ошибку типа:

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

то это лечится вот так:
localedef --no-archive -i ru_RU -c -f UTF-8 ru_RU.UTF-8