It is always a good idea when developing big games to keep the things outside the core nice and scriptable, it makes them a lot easier to change and also allows external developers to more easily bang out things like the Quake mods, TCOs, and even the huge Baldur's Gate add-ons which are freely available

Perl should be a nice plugin language for scripting though, and with XS for your C++ integration (And Inline::CPP for your quick tests) you should be able to manage wonders.

There is a nice tutorial on developing your own 'little language' for scripting in the Tutorials section of Flipcode. Whilst it probably won't help you with the technical implementation it will give you a nice overview of some considerations which you may otherwise overlook. It's the 'Scripting Language Tutorials Series', and it's worth a quick look at least in my opinion.