There is an ongoing outage on the primary CPAN mirror. It is possible to work around the issue by using MetaCPAN as a mirror.
Encode::CJKConstants.pm -- Internally used by Encode::??::ISO_2022_*
To install Encode, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Encode
CPAN shell
perl -MCPAN -e shell install Encode
For more information on module installation, please visit the detailed CPAN module installation guide.