Classical Tibetan is a deliberately engineered literary language. Tibetan tradition credits the minister Thonmi Sambhota, sent to India by the seventh century emperor Songtsen Gampo, with devising the Tibetan script on an Indian model, and the empire then undertook one of history's great translation projects, turning the Buddhist literature of Sanskrit into Tibetan. In the early ninth century the work was standardized by imperial decree. Revisers fixed the orthography, and a Sanskrit Tibetan glossary, the Mahavyutpatti, established equivalents for thousands of technical terms so that every translator would render a given Sanskrit word the same way. The result is a translation language of extraordinary consistency, so regular that scholars routinely reconstruct lost Sanskrit originals from the Tibetan.
Because the spelling was fixed while the spoken language kept evolving, Classical Tibetan orthography now sits far from modern pronunciation, and the written register unites readers across Tibet, Bhutan, Nepal, northern India and Mongolia whose spoken varieties differ widely. The canon this register carries, the Kangyur of translated Buddha word in roughly a hundred volumes and the Tengyur of translated treatises in more than two hundred, preserves an immense Indian Buddhist library whose Sanskrit originals largely perished.