In the 2005 documentary, The Boy with the Incredible Brain, producers introduced Daniel Tammet, a young British savant with tremendous cognitive skills. The producers tested his abilities, and one challenge required Tammet to learn Icelandic in less than a week.
In his memoir, Tammet wrote how he worked with a dictionary, flashcards and then eventually a tutor. He instantly memorized words and quickly recognized grammar rules and sentence structure. By the end of the week, Tammet proved his fluency in an interview on an Icelandic news show.