This Chinese-Tibetan Lankavatara Sutra is one of the most interesting, and beautiful bilingual manuscripts from Dunhuang. As the picture above shows, it was made in the concertina format. The Chinese text, written in black ink, is a commentary on the Lankavatara Sutra, while the Tibetan text, written in red ink between the lines of Chinese, is the Tibetan translation of the sutra itself (but not the commentary).
When you read the Chinese text on this manuscript, you treat the concertina as if it were a folded Chinese scroll (which it basically is), reading from top to bottom and right to left:
On the other hand, in order to read the Tibetan, you have to turn the manuscript ninety degrees to the left, and read from left to right. When you do this, the concertina looks much more like a Tibetan pothi, and there is even a string-hole to make that association quite clear:
If you look carefully at these images, you can see that the text has been carefully marked up to show where the Tibetan translation corresponds to the Chinese. So what was the manuscript used for? One possibility is that it was used by someone learning Tibetan, or Chinese.
Another very interesting theory, suggested by Daishun Ueyama, is that this manuscript was used by the translator Chodrup, who lived in Dunhuang in the 9th century, and produced several translations of Buddhist texts into Tibetan from Chinese. Since the Tibetan text on this manuscript is from a different translation of the Lankavatara Sutra, made from a Sanskrit text, the manuscript could have been used in the course of preparing a new translation from Chinese.References
Manuscript: Or.8210/S.5603, Stein Collection, British Library.
Ueyama Daishun. 1990. Tonkō bukkyō no kenkyū [Studies on Buddhism in Dunhuang]. Kyōto: Hōzōkan.