Tell why you think Python, Perl, Ruby, etc is easiest for plugging in modules from other languages with minimal thought.
To clarify, an example: I want to write business logic in Python, but use functionality that conveniently exists as a Perl module.
In other words, which language "just works" with the most modules?
The Dynamic Language Runtime was specifically designed to allow one dynamic language to use objects and functions defined in another dynamic language. Currently Python and Ruby have DLR implementations, but I haven't heard anything about Perl.
To use the DLR you need either .NET or Mono.
Which dynamic language can easily use libraries from other languages?