Oh, yeah; I'm just not convinced there's any particular reason to think that LLMs would be useful for decoding languages.
(That said it would be an interesting _experiment_, if a little hard to set up; you'd need a live language which hadn't made it into the LLM's training set at all, so you'd probably need to purpose-train an LLM...)
LLMs are.. not bad at finding some semantic relationships between some arbitrary data. Sure, if you dump an unknown language into LLM then you can only receive a semantically correct sentences of unknown meaning, but as you start to decode the language itself it would be way easier to find the relationships there, if not just outright replacing the terms with a translated ones.
(That said it would be an interesting _experiment_, if a little hard to set up; you'd need a live language which hadn't made it into the LLM's training set at all, so you'd probably need to purpose-train an LLM...)