It appears, when Perl prints to binary STDOUT, it tries to encode some strings as Latin-1
perl -wE 'use utf8; say q(Franšais)' | perl -lnwE 'print join q(:), un
+pack q(C*), $_' -
char 241 is not valid utf-8. Interestingly enough...
perl -wE 'use utf8; say q(Русский)' | perl -lnwE 'print join q(:), unpack q(C*), $_' -
Wide character in say at -e line 1.
... which is valid utf-8... and a warning.
Well... what do you expect? Even this site mangles utf-8 characters in 'code' tags, if it cannot decode them as Latin-1.
I think perlmonks is written in Perl ;) Yes, that's all pretty mysterious and confusing.