Comment by Mark on "How do I learn to create an Object Oriented Programming Language?"

Think about what will make your language special. Why would people use yours instead of Java, Smalltalk, Self, IO...
Realize that there is a 99.9% chance that fewer than 20 people will use your language for anything, ever. There have been a lot of languages, this list only mentions the popular ones, and even most of those we've never heard of. There are at least 10x as many failed ones (but who knows, could be 1000x). It's still a great project, and you'll learn a lot - if that is enough, then I highly recommend going for it!
You need to choose where your code gets run: an interpreter like (typical) Python, compiled like C++, on a VM (maybe even the JVM) like Java, JIT'ed, or in a browser like Dart. You can do multiple, but you won't have time for that.
There are some complexities for object oriented languages, but it's not the majority. You'll have to learn e.g.
- How virtual calls are implemented (then you call interface.method), usually vtables.
- How to do type casts (do you save types at runtime?).
- How variance works, especially with generics.
- How to resolve the diamond problem, if you support multiple inheritance (Java doesn't).
You might want to be aware that several new languages, like Rust and Go, don't have inheritance. While still popular and useful, OO (inheritance, at least) is over its peak, and some people feel it is not as great as initially believed. Take that into account. (Others like Yegor still like it and feel Java didn't go far enough).
Besides these OO-specific concerns, most of the effort will the same for non-OO language design. You can read more in this question.

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