There are two types of plugin:

Plugins can be written in any language you choose. 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 or your users want to use plugins written in a scripting language you will, of course, need to have the appropriate scripting engine installed. Here are where you can get some of them: