I have an acquaintance who was taught Chinese in the Air Force. The training was even more intense than the article describes. He was immersed in Chinese language 24 hours per day, having to wear earphones, while sleeping, that continued the immersion.I remember, years ago, a conversation with a woman whose sister was in the foreign service. She told me that the foreign service has precise ratings of people's level of fluency in foreign languages. (I think Concerned Parent knows all of this & may be rated or ranked herself. Hope she's around.)
Twenty years later, when he dreams, it's in Chinese.
As I recall, I think there is a very small group of non-native speakers who reach the level of native fluency.
(Is that right?)
Here are Foreign Service Institute courses in the public domain
And here's the book on second language learning Lefty recommended to me: Handbook of Research in Second Language Teaching and Learning by Eli Hinkel.