What programming language is Windows based on

Answer 1

The .NetFramework
C#

Answer 2

Consequently, the programming languages used are nearly all the major programming languages you may find in any of today's (large or small) software projects, such as: C/C++, C#/ Java, ASP-Dot-Net, JavaScript, F#/ ML,Lisp/Smalltalk/Clojure, VB, Assembler, etc

. https://social.microsoft.com/Forums/en-US/65a1fe05-9c1d-48bf-bd40-148e6b3da9f1/what-programming-language-is-windows-written-in?forum=windowshpcacademic