When would you use multiple languages in one project? [closed]

Question

When would you consider incorporating another language into your project? Some domains are inherently multi-language ( Database interaction, interactive web client side development), but others could be done with 1 language and the idea of introducing another language could hinder understanding more than help it.

Currently I have high performance code in C++ that also needs to do a fair amount of routine file and i\o manipulation which would be easier and faster to write correctly in a higher order language like Python. To be honest I don't know C++ extremely well when it comes to 3rd party libraries including Boost.