Esta dica vale para o Debian do Raspberry, o Raspian, assim como o Debian do Rock64, entre outros.
dpkg-reconfigure locales
E isto resolve qualquer dos problemas abaixo apresentado:
perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LANG = "en_US.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C"). locale: Cannot set LC_CTYPE to default locale: No such file or directory locale: Cannot set LC_MESSAGES to default locale: No such file or directory locale: Cannot set LC_ALL to default locale: No such file or directory /usr/bin/locale: Cannot set LC_CTYPE to default locale: No such file or directory /usr/bin/locale: Cannot set LC_MESSAGES to default locale: No such file or directory /usr/bin/locale: Cannot set LC_ALL to default locale: No such file or directory