English is an incredibly difficult language to learn. It takes several years of study to become literate. You don't need to have fluency in English to use Perl; you could learn the keywords by rote. For the rest of the documentation you need, you could use machine translation (or better yet, resources in your native language!).
There is plenty of value in having documentation in other languages. Perhaps such documentation will intrigue someone to learn Perl when they would have turned to some other programming language. I imagine more than a few of the 1.3 billion speakers of Chinese will benefit from this book, as will the Perl community from their eventual contributions.
"The vast majority of software and documentation is written in English, like it or not."
Fayland is trying his best to rectify that! The computer science field has far more than its fair share of Anglocentrism as it is.