What language would you recommend for scripting

You make plugins using C++ and execute them via the application when the plugin is installed, to my knowledge.
Otherwise you can execute a script or plugin using any language that can execute a file:

For javascript, this is done by executing the javascript file within the context of the Illustrator application: example is VB and its "DoJavaScript" method. VB has type library support for Illustrator, so it can work.

For executing a C++ plugin, same thing, and inside javascript there is a special "sendScriptMessage" function which can take some arguments and relay them from javascript into the application which can then pass the to a C++ plugin. Typically this works good because it takes a lot more time and technical knowledge to do C++, but not as much when doing Javascript: a C++ person can create low-level features which a JavaScript person can quickly utilize using their JavaScript skills in many different ways. As an example, a C++ plugin can do something complex and impossible with regular scripting, but a script can take that feature and run it inside of a loop.