Bailey was born in Devizes, Wiltshire, and raised from age 10 onwards on a farm in western Australia without formal education. While growing up, he learned German, Italian, Spanish, Latin, and Greek from household books, and Russian from a neighbor. After he grew interested in the lettering on tea-chests from India, he acquired a book of Bible selections translated into languages with non-European scripts, including Tamil, Arabic, and Japanese. By the time he had left home, he was reading Avestan as well….
Bailey has been described as one of the greatest Orientalists of the twentieth century. He was said to read more than 50 languages, and was the world’s leading expert in Khotanese, the mediaeval Iranian language of the kingdom of Khotan in Chinese Turkestan. He was known for his immensely erudite lectures, and once confessed: “I have talked for ten and a half hours on the problem of one word without approaching the further problem of its meaning.” …
But there is much more detail in the Encyclopaedia Iranica biography and bibliography by John Sheldon:
His parents decided to emigrate to Western Australia and bought 805 acres of virgin bushland about two hundred kilometres east of Perth. Hence it was that Harold Bailey never again attended a school, but worked with the other members of his family to clear the land and turn it into a farm. His spare time was devoted to reading and he devoured everything that he could find starting with the eight volume Harmsworth Encyclopaedia in which he first read about “Teheran” and “Avestan” and four other books containing lessons in French, Latin, German, Greek, Italian and Spanish. In 1919 he seems to have gained access to books in Sanskrit, Pali and Avestan… Bailey’s extraordinary ability to remember any word he had seen in any language, which was described by many of the most erudite of his peers in later life as “phenomenal”, was without doubt in evidence in his youthful years. The extent of the knowledge he had somehow acquired can be gauged by the fact that he managed during his early time at the university to compose a long Sanskrit poem in the mandākrāntā metre….