in reply to perl 5.8.4 threads

Be aware that Perl's ithreads are quite different from Python's threads, and much, harder to use well.

Python's threads are "user threads" whereas Perl's are "kernel threads". Google for many good descriptions of the difference and the pros and cons of both.

... my perl told me that I need 5.8.6 ...

Tell "your perl" it's wrong. Perl has had threads since 5.6.1 and usable threads since 5.8.4, though it is correct that if you are going to use threads, it would be a good idea to get the latest version.

why perl do not have predefined thread as in python.

You have to do from threading import Thread to use threads in Python and use threads; to use threads in Perl. What difference?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.

In Section Seekers of Perl Wisdom