I assume that after careful consideration you have chosen Perl to be a good substitution for 4D, otherwise of course there is no reason why you should switch to Perl.

The second thing you should think of, is whether you already have an exhaustive test suite for your existing 4D-application?

Indeed, even if it is possible to do a machine translation (and other monks have already pointed out that it is by no means certain/efficient/desirable), you will still need to verify that indeed the translated application runs correct.

Without a good test suite there is no way that you can even be remotely certain that the Perl programs faithfully emulate your 4D code.

A good book to read is Perl Medic: it is all about transforming legacy code.

Update: Of course it is about Perl legacy code but the concepts touched upon in the book are valid outside the Perl realm as well.