Yi script
The Nuosu language, spoken in southern China, is written with its own script, the Yi script. The only existing romanisation system is YYPY (Yi Yu Pin Yin), which represents tone with letters attached to the end of syllables, as Nuosu forbids codas. It does not use diacritics, and as such due to the large phonemic inventory of Nuosu, it requires frequent use of digraphs, including for monophthong vowels.