Who implements transliteration rules? I assume operating systems? Or text renderers?

The ICU library. It’s so ubiquitous that it’s somewhat difficult to avoid this library if you are doing anything advanced with human text.

	▲	ks2048 2 hours ago \| parent [-]
		And ICU uses data from CLDR, which is mentioned in the blog. Here, there are 380 xml files: https://github.com/unicode-org/cldr/tree/main/common/transfo... Yes, ICU is ubiquitous. But, some NLP projects use various other libraries, such as uroman (just for romanization - to Latin script).