Actually, if you are using a modern (5.8) perl, the internal format is utf8 (or close enough, IIRC it is actually a superset of utf8).

Almost. The standard character set is UTF-8 (case-insensitive, with a dash).

The internal format is locally known (non-standard, Perl-only) as utf8. It's a superset of UTF-8 capable of representing all 32-bit or 64-bit numbers (depending on the system, for some definition of system).