Assembly -> C is not the same as C/Python/Java -> Natural Language. C is not a natural language, so there is no ambiguity in C code (undefined behavior does not really count). Compilers that can compile from one programming language to another exist today. I can imagine an LLM being used to speed up the building of this compiler, but even here, like in self-driving, the hard part is going to be ensuring 100% accuracy, which the LLM seems particularly ill-suited for.