It doesn’t have to be a totally new language. Javascript is an example where there are multiple front-end languages. You can go as far as formally prove the implementation is correct, too. Language theory is an abstraction for mathematical logic and proofs, so it touches anything logical at all.
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I agree with the first sentence. I don't think in 2023 a new programming language will help humans in a significant way.
It doesn’t have to be a totally new language. Javascript is an example where there are multiple front-end languages. You can go as far as formally prove the implementation is correct, too. Language theory is an abstraction for mathematical logic and proofs, so it touches anything logical at all.