Do you know of any work being done on the idea of bringing in code from other languages like Perl, PHP, Python, etc.? That is, import the code in some way and then convert it to Mathematica code?
No, Mathematica has no built-in ability to do this. I am not aware of any packages either, though there might be some limited ones.
What you can do is call code written in other languages from Mathematica. I am aware of interfaces to C/C++, Java (and other JVM-based languages), .NET (see all three here), R, MATLAB, Clojure, NetLogo, Python (limited). There are probably several others.