tl;dr: We need a language-design tag. For already created languages.
We have tags for interpreter and tags for compiler, so I think that a language-design, or something similar to the likes of that. There are already quite a few questions, like this one that would suggest the need for a tag like this. So, in short, I think a tag for language design should be implemented. As usual, it would require that the language has been created, and that it's sources is in the question.
I'm not sure we need more design-oriented tags, at least not one like this.
Design in general is mostly off-topic and some are surely going to misuse it. Regarding the question you've referenced, why doesn't interpreter suffice? It's also based on a custom language which are harder to review, but I digress. If you still think it would be a good tag, then at least more good examples may be needed. You could also mention what value it would add. Simply referencing interpreter and compiler and nothing else isn't very helpful, and could possibly suggest that they (in addition to any similar ones) are enough.
Pure design questions are off-topic for Code Review. And importantly, no matter how much code you include, a question about designing a language can't possibly be on-topic for Code Review.
Code Review requires real, working code.
If there is nothing to interpret/compile the code, the code can't be real or working. Your language is nothing more than a special syntax for pseudo-code.
If there are still design questions for the language (or what an upcoming version of the language might look like), those design aspects can't possibly be already implemented in an interpreter/compiler.
Theoretically, once you get an interpreter/compiler going, you could sort of cheat the system slightly by posting some code written in your language for you review and appending something like:
Oh by the way, I'm the language designer, so any critique of the language syntax or mechanics would be appreciated as well.
But you'd have to be careful with this. If this is the core of your question, I'd be likely to vote to close.
Questions about design in general, and designing a language in specific, can be potentially on topic on Programmers, but of course, don't take my word for it, read their help center and visit their meta.
