Reading through John Michael Greer’s new blog, I find mention of Joseph Jacotot.
“He was assigned to teach a class in the Alsace; half the pupils spoke only French, half only German. In desperation, he had them memorize the same passages of prose in both languages, and found that they very quickly became bilingual. He proceeded to create a method on that basis. In my experience, it works very well — your brain very quickly picks up the tricks of grammar and syntax by memorizing complete passages, and since you know what’s being said, it’s easy to absorb the whole pattern.”