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.

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).