in reply to
How to generate random sequence of UTF-8 characters
A random sequence of all possible UTF-8 characters? That is going to be quire a huge string.
Anyway, don't worry about UTF-8. You must just create characters, which you can do with chr($code), where $code is an integer, a valid UNICODE character code point, which is basically any value between 0 and 0x10FFFF — except some of those will represent unprintable characters, such as control characters, and you probably don't want those.
Let Perl worry about converting it to UTF-8.