I think we assume that a complex language is dependent upon some system of writing to exist.
But try getting my four-year-old grand daughter, who can barely write her own name, to stop talking and she uses very complex language. The other day, her mum was suggesting that they do something, and Kaya replied,
"Yes, Mummy ... but beforehand, we should do .... etc"
She'll be saying 'notwithstanding the aforementioned' next!