There are two types of plugin:
Plugins can be written in any language you want. The only requirement is that you be able to read a Windows INI file and can write to the console. Popular choices are scripting languages such as Python or Perl but you could also use Java, C++ or C#!
If you want to use plugins written in a scripting language you will need to have the appropriate scripting engine installed. Here are where you can get some of them: