He cannot remember being unable to read, not in English or French at any rate, although Mycroft assures him that there was a time in his infancy when 'devouring a book' was a matter of gums and the occasional tooth rather than an intellectual exercise. Arabic, Greek, and Cyrillic characters slowed him only briefly – his ear for phonemes is exceptionally fine, and alphabetical systems are logical, even when the languages they represent are not so clear. As he ventures deeper into the East, however, he is encountering books which refuse to be read.
Tibetan is going to be a problem.