Mongolian writing systems

Many alphabets have been devised for the Mongolian language over the centuries, and from a variety of scripts. The oldest, called simply the Mongolian script, has been the predominant script during most of Mongolian history, and is still in active use today in the Inner Mongolia region of China and de facto use in Mongolia. It has spawned several alphabets, either as attempts to fix its perceived shortcomings, or to allow the notation of other languages, such as Sanskrit and Tibetan. In the 20th century, Mongolia first switched to the Latin script, and then almost immediately replaced it with the Cyrillic script for compatibility with the Soviet Union, its political ally of the time. Mongol chinese in Inner Mongolia and other parts of China, on the other hand, continue to use alphabets based on the traditional Mongolian script.

The Xianbei spoke a proto-Mongolic language and wrote down several pieces of literature in their language. They are believed to have used Chinese characters to phonetically represent Xianbei like the Japanese system of Man'yōgana but all works written in Xianbei are now lost.

The Khitan spoke a proto mongolic language called Khitan language and had developed two scripts for writing their language: Khitan large script, a logographic script derived from Chinese characters, and Khitan small script, derived from Uighur.

At the very beginning of the Mongol Empire, around 1204, Genghis Khan defeated the Naimans and captured an Uyghur scribe called Tata-tonga, who then adapted the Uyghur alphabet—a descendant of the Syriac alphabet, via Sogdian—to write Mongol. With only minor modifications, it is used in Inner Mongolia to this day. Its most salient feature is its vertical direction; it is the only vertical script that is written from left to right. (All other vertical writing systems are written right to left.) This is because the Uyghurs rotated their script 90 degrees anticlockwise to emulate the Chinese writing system.

...
Wikipedia