Hello Eric,
as geni has explained, the Wikimedia Foundation tends to launch broad projects over narrow ones: Wikipedia over "an encyclopedia of birds", Wikinews over "a news site about health issues", Wikisource over "public domain novels", and so on.
Much of the content of an "encyclopedia of Perl" would likely have a place in our existing Wikipedia and Wikibooks projects. For source code, there's also an interesting wiki at: http://en.literateprograms.org/
What would be the justification for starting a new separate Wikimedia site just for Perl? Mind you, nothing will stop you from setting up your own site using the MediaWiki software (except maybe an aversion to PHP ;-). You can also use a wiki hosting service, like the ones listed at: http://en.wikibooks.org/wiki/Wiki_Science:How_to_start_a_Wiki
Erik