I mean natural language as "language for humans to use to communicate with each other" as opposed to programming language as "language for humans to use to communicate with computers". It's the same meaning as is used in NLP.

e.g. https://en.wikipedia.org/wiki/Hangul https://en.wikipedia.org/wiki/Cyrillic and I guess even https://en.wikipedia.org/wiki/Klingon_language

This is different than the meaning of https://en.wikipedia.org/wiki/Natural_language and https://en.wikipedia.org/wiki/Constructed_language

I guess if you want to get pedantic a better term might be "Orthographic design".