Regular expressions in JavaScript have various features to support internationalization. In some cases, these features are defined with reference to the Unicode Standard. For example, the Canonicalize algorithm used to define case-insensitive (/i) RegExps refers to the CaseFolding.txt file of the Unicode Character Database.
The ICU4X project provides components for internationalization written in Rust. This crate builds on ICU4X to provide access to the Unicode data necessary to implement a regular expression engine compatible with the ECMA262 standard.