There is an assumption that any kind of logic construction interface is a programming language , that simply is not the case
a programming language, usually, is turing compete, what that means is that it passes the turing test, what that means is that is do any kind of logic.
There are several cases however even in text coding that this is simply not true, like DSL , Domain Specific Languages, these language are not programming languages and instead they are used for very specific scenarios like HTML.
How complex the language is depends solely on how much freedome the language gives. If its very limited it will be also very easy to implement.
But even in the case you want to implement a full blown blueprint it can be dead easy. How you make something extremely complex to extremely easy ? Automation of course. Or to put it more plainly you “steal” code.
Online you will find A TON of visual language that are coded in C++ or other language that can be used for what you want to do. The tricky part is doing the GUI since the language itself is given and of course warping your game objects to the language.
Ideally you could hack the editor itself to be included with your game and provide blueprint scripting directly, afterall UE is open source for this reason.