R. G. Loeliger Threaded Interpretive Languages Their Design And Implementation[1] is an amazing book, since it was out of print, I printed it on a good 160gsm a4 paper, and I randomly open it every few weeks just to read through it. I strongly recommend it, even if you are not interested in Forth.
I have been programming in all kinds of languages, from assembly to clojure, but in 25 years I never programmed stack languages, I was kind of scared of them, it wasn't until I read the book and made my own Forth I understood what I was missing. Since then I made few interpreters, with jit, or with types, etc, it was super fun, but most of all it allowed me to see a completely new paradigm of programming, kind of the first time you understand eval/apply from 13th page of the LISP 1.5 Programmer's Manual. A language that writes itself and it is written in itself.
If you are making your own Forth, this Brad Rodriguez's article is also really good [2].
[1]: https://archive.org/details/R.G.LoeligerThreadedInterpretive...