Consider Schliemann's methods of learning Greek:
...My wish to learn Greek had always been great, but before the Crimean war I did not venture upon its study, for I was afraid that this language would exercise too great a fascination over me and estrange me from my commercial business; and during the war I was so overwhelmed with work, that I could not even read the newspapers, far less a book. When, however, in January 1856, the first tidings of peace reached St. Petersburg, I was no longer able to restrain my desire to learn Greek, and at once set vigorously to work, taking first as my teacher Mr. Nicolaos Pappadakes and then Mr. Theokletos Vimpos, both from Athens, where the latter is now archbishop. I again faithfully followed my old method; but in order to acquire quickly the Greek vocabulary, which seemed to me far more difficult even than the Russian, I procured a modern Greek translation of Paul et Virginie, and read it through, comparing every word with its equivalent in the French original. When I had finished this task, I knew at least one-half the Greek words the book contained, and after repeating the operation I knew them all, or nearly so, without having lost a single minute by being obliged to use a dictionary. In this manner it did not take me more than six weeks to master the difficulties of modern Greek, and I next applied myself to the ancient language, of which in three months I learned sufficient to understand some of the ancient authors, and especially Homer, whom I read and re-read with the most lively enthusiasm.
I then occupied myself for two years exclusively with the literature of ancient Greece; and during this time I read almost all the classical authors cursorily, and the Iliad and Odyssey several times. Of the Greek grammar, I learned only the declensions and the verbs, and never lost my precious time in studying its rules; for as I saw that boys, after being troubled and tormented for eight years and more in schools with the tedious rules of grammar, can nevertheless none of them write a letter in ancient Greek without making hundreds of atrocious blunders, I thought the method pursued by the schoolmasters must be altogether wrong, and that a thorough knowledge of the Greek grammar could only be obtained by practice --that is to say, by the attentive reading of the prose classics, and by committing choice pieces of them to memory. Following this very simple method, I learnt ancient Greek as I would have learnt a living language. I can write in it with the greatest fluency on any subject I am acquainted with, and can never forget it. I am perfectly acquainted with all the grammatical rules without even knowing whether or not they are contained in the grammars; and whenever a man finds errors in my Greek, I can immediately prove that I am right, by merely reciting passages from the classics where the sentences employed by me occur.
Similarly, consider his methods of learning English and the Romance languages, which go quite beyond what most ordinary language learners would do:
...I applied myself with extraordinary diligence to the study of English. Necessity taught me a method which greatly facilitates the study of the language. This method consists in reading a great deal aloud, without making a translation, taking a lesson every day, constantly writing essays upon subjects of interest, correcting these under the supervision of a teacher, learning them by heart, and repeating in the next lesson what was corrected on the previous day. My memory was bad, since from my childhood it had not been exercised upon any object; but I made use of every moment, and even stole time for study. In order to acquire a good pronounciation quickly, I went twice every Sunday to the English church, and repeated to myself in a low voice every word of the clergyman's sermon. I never went on my errands, even in the rain, without having my book in my hand and learning something by heart; and I never waited at the post-office without reading. By such methods I gradually strengthened my memory, and in three month's time found no difficulty in reciting from memory to my teacher, Mr. Taylor, in each day's lesson, word by word, twenty printed pages, after having read them over three times attentively. In this way I committed to memory the whole of Goldsmith's Vicar of Wakefield and Sir Walter Scott's Ivanhoe. From over-excitement I slept but little, and employed my sleepless hours at night in going over in my mind what I had read on the preceding evening. The memory being always much more concentrated at night than in the day-time, I found these repetitions at night of paramount use. Thus I succeeded in acquiring a thorough knowledge of the English language.
I then applied the same method to the study of French, the difficulties of which I overcame likewise in another six months. Of French authors I learned by heart the whole of Fenelon's Aventures de Telemaque and Bernardin de Saint Pierre's Paul et Virginie. This unremitting study had in the course of a single year strengthened my memory to such a degree, that the study of Dutch, Spanish, Italian and Portuguese appeared very easy, and did not take me more than six weeks to write and speak each of these languages fluently.