Richard Burton's technique

Sir Richard Burton, the great 19th century British adventurer who penetrated the forbidden sacred cities of Islam, discovered Lake Tanganyika, explored the Amazon and shocked Victorian England with his detailed reports on sex practices in distant lands, was  also one of the great linguists of his time. A distinguished translator from Hindi, Portuguese, Arabic and several other languages, he was said to be able to pass for a native in 29 languages, and to have developed a technique for learning a new language which Burton described in his memoirs:

"My system of learning a language in two months was purely my own invention, and thoroughly suited myself.

I got a simple grammar and vocabulary, marked out the forms and words which I knew were absolutely necessary, and learnt them by heart by carrying them in my pocket and looking over them at spare moments during the day. 

I never worked for more than a quarter of an hour at a time, for after that the brain lost its freshness.
After learning some three hundred words, easily done in a week,
I stumbled through some easy bookwork (one of the Gospels is the most come-atable), and underlined every word that I wished to recollect, in order to read over my pencillings at least once a day.
Having finished my volume, I then carefully worked up the grammar minutiae,
and I then chose some other book whose subject most interested me.
The neck of the language was now broken, and progress was rapid.

If I came across a new sound, like the Arabic Ghayn, I trained my tongue to it by repeating it so many thousand times a day. When I read, I invariably read out loud, so that the ear might aid memory.
I was delighted with the most difficult characters, Chinese and Cuneiform, because I felt that they impressed themselves more strongly upon the eye than the eternal Roman letters. This, by-and-by, made me resolutely stand aloof from the hundred schemes for transliterating Eastern languages, such as Arabic, Sanscrit, Hebrew and Syriac, into Latin letters,
and whenever I conversed with anybody in a language that I was learning, I took the trouble to repeat their words inaudibly after them, and so to learn the trick of pronunciation and emphasis.”

Burton's readiness to admit his stumbling and his short attention span brings him closer to us and makes us want to sort out what is illusory and what is real in the Burton legend.

Don't be misled by reputation. Perhaps Burton was an utter master of all of his 29 languages. But reputations are often overdone. Burton himself was well aware of the difference between mastering a language and merely being able to say "please" and "thank you" in it. He never claimed for himself even a small part of what his idolators claimed for him.