I read that Tk is on its 8.5 version. Why do I find only the 8.4 version with Perl (cpan, Activestate)?

You need to use perl version 5.10 or higher to get 8.5 Tk tutorial

I guess the closest thing to Perl/Tk is Tkx. Anyone experienced ith translating any big project? Is it a big pain?

They say...
"The "ActivePerl" distribution from ActiveState includes not only Perl, but also recent versions of Tk and Tcl (which Tkx uses internally to talk to Tk)."