Forth, PostScript and Assembly are the "natural" programming languages from the perspective of how what you express maps to the environment in which the code executes.

The question is "natural" to whom, the humans or the computers?

AI does not make human language natural to computers. Left to their own devices, AIs would invent languages that are natural with respect to their deep learning architectures, which is their environment.

There is always going to be an impedance mismatch across species (humans and AIs) and we can't hide it by forcing the AIs to default to human language.