The difficulty wasn't in the engine. JS itself is just as good with accepting Unicode characters as Rust, both in code and strings. The problem was with the PEG

The difficulty wasn't in the engine. JS itself is just as good with accepting Unicode characters as Rust, both in code and strings. The problem was with the PEG implementation. Without some sort of shorthand for Unicode families, defining programming languages that are valid in multiple real-world languages becomes a serious burden.