Yes and if you withhold anything in Japanese language from the training set, the LLM will be quite lousy at writing in Japanese even if you put some language co

Yes and if you withhold anything in Japanese language from the training set, the LLM will be quite lousy at writing in Japanese even if you put some language coursebook into its context. I'm not sure what this is supposed to prove. There is a reason why stuff is put into the training set and that training is done. A regular person also won't be putting together perfect Japanese sentences even with the grammar book. But if they learn it deeper into their "brains" (analogy of the training phase as opposed to just putting an explanation into the context window), then they will be better at it.