Mongolian Haa and What an Inherited Alphabet Cannot Do

Every borrowed script reaches a limit. The Mongolian alphabet was taken from Old Uyghur because it worked for the Mongolian language, and it did, but the moment it was asked to write Sanskrit, Tibetan and Chinese accurately it began to run out. Adding letters solves part of the problem and not all of it. A letter can be supplied for a sound the receiving language lacks. It is harder to supply a way of writing a consonant cluster the receiving language does not permit, or a syllable structure it does not have, or a tone it does not use, because those are properties of how sounds combine rather than of the sounds themselves. The Mongolian additions show the tradition working outward from the easy cases to the hard ones: first single consonants, then a cluster sign, then two signs standing for whole syllables of Chinese.

Beyond the alphabet, the apparatus encoded in Unicode under the name Ali Gali goes further still, providing what is needed to write Sanskrit and Tibetan in full. What none of it does is turn the Mongolian alphabet into an Indian one, and the distinctions Indian phonology draws remain awkward in it. That is the honest position of any script writing a language it was not built for.