Language Acquisition without Speaking and without Study.

Massive, compelling, self-chosen input may be key to language acquisition. This article refers to video input, but the same case has been made for extensive reading.

Christy Lao and Stephen Krashen
Journal of Research of Bilingual Education Research and Instruction 16(1): 215-221. 2014.
This paper describes a case of second language acquisition without speaking, without instruction, and without any kind of study. The subject, in fact, disdained study.
Paul is a young man, now a teenager, growing up in a Cantonese-speaking family in California. His parents are both native speakers of Cantonese, but highly proficient in English, and his mother speaks Mandarin very well. His grandparents live with the family and speak Cantonese with Paul and his brother.
Cantonese and Mandarin are different languages. They are related, and share some common vocabulary, but they are not completely mutually comprehensible. With the help of context, Cantonese speakers are able to understand a limited amount of Mandarin and vice versa.
Today, as a teenager, Paul speaks Mandarin quite well, in addition to Cantonese and English. He has a Cantonese accent when he speaks Mandarin and makes only a few errors. When Mandarin-speaking guests are at his home, he has no trouble conversing on everyday topics, and on occasional visits to China with his family he is comfortable speaking Mandarin.
This paper describes how Paul did it. Nearly all of his exposure to Mandarin has been through media, through TV and CD’s, with no classes, no study, and no interaction.
When Paul was a baby, his grandmother took care of him most of the time. Grandma liked to sing Paul lots of Cantonese and Mandarin songs and they watched Chinese MTV for children, which was in Mandarin.

source: Krashen