Locales are used in Linux to define which language and character set (encoding) the user uses.
Can't set locale; make sure $LC_* and $LANG are correct! perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LC_TIME = "de_DE.UTF-8", LC_MONETARY = "de_DE.UTF-8", LC_ADDRESS = "de_DE.UTF-8", LC_TELEPHONE = "de_DE.UTF-8", LC_NAME = "de_DE.UTF-8", LC_MEASUREMENT = "de_DE.UTF-8", LC_IDENTIFICATION = "de_DE.UTF-8", LC_NUMERIC = "de_DE.UTF-8", LC_PAPER = "de_DE.UTF-8", 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_ALL to default locale: No such file or directory Gtk-WARNING **: Locale not supported by C library.
A quick and simple solution is to execute this and maybe add it to your .bashrc file in your /home folder:
If this does not fix your problem check and generate the missing locales on Debian with
locale sudo dpkg-reconfigure locales