Предупреждение локали во время выполнения adduser

Я просто попытался добавить пользователя в группу

$ adduser someuser sudo
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = "en_US:en",
    LC_ALL = (unset),
    LC_PAPER = "pl_PL.UTF-8",
    LC_ADDRESS = "pl_PL.UTF-8",
    LC_MONETARY = "pl_PL.UTF-8",
    LC_NUMERIC = "pl_PL.UTF-8",
    LC_TELEPHONE = "pl_PL.UTF-8",
    LC_IDENTIFICATION = "pl_PL.UTF-8",
    LC_MEASUREMENT = "pl_PL.UTF-8",
    LC_TIME = "pl_PL.UTF-8",
    LC_NAME = "pl_PL.UTF-8",
    LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
Adding user `someuser' to group `sudo' ...
Adding user someuser to group sudo
Done.

Что это значит, что пошло не так и как устранить ошибку?