Windows includes JScript and VBScript with the Windows Script Host but you can install other script engines. Such an engine would probably need to identify itself using a name other than “JScript” to avoid conflicts with the Windows Script Host version of JScript. The script engine's name is what you insert in a macro inside the MCR file used by XMetaL Author to let it know which script engine to tell Windows Script Host to use to run the script for that particular macro.
Whether such an engine exists for Windows I don't know. It needs to meet these requirements: https://docs.microsoft.com/en-us/scripting/winscript/windows-script-engines
This would be similar to people that install and use the PerlScript (ActivePerl) or PythonScript (ActivePython) engines with XMetaL Author. Most people are using JScript or VBScript as they do not require additional software to be installed, but there are a number of XMetaL Author users that do use these other engines.