What exactly is the secret behind creating your own languages in general

Answer 1

Idk much about creating custom language
But. This might help on your question
https://cs.stackexchange.com/questions/71473/what-does-being-turing-complete-mean

Answer 2

Knowing your target use cases and making good decisions about abstractions.

Not sure if that's the kind of secret you were looking for, but I hope this helps! 😊