You don't need to hire an expert in language X, you can and should look for expert programmers that are willing to learn language X

While I applaud this approach, it is not without its risks. I was once hired as a Java programmer even though I had no Java experience. I learnt Java easily enough, but resigned soon after when I realised that I did not like Java or its culture. That was an expensive hiring mistake. So you'd need to be confident that the job applicant would like Perl and its culture before hiring.

An expert can easily cross over from being a novice in any language in a matter of a few weeks

Maybe some experts can do that, but not the average programmer, at least according to a study reported in Peopleware (chapter 8) where they found the statistical productivity sweet spot from their sample of over 600 developers in a coding competition was reached not in a few weeks, but after six months experience.