This might seem like an obvious question, but wouldn't it be more effective for the README to be in Korean? Not that having it in English too is a bad thing, but people interested in a language with Korean keywords probably can read Korean more comfortably than English (if they can read English at all).
Anyway, I don't really see why PLs that support UTF-8 idents can't just reserve multiple aliases in different languages for their keywords. Rust is mentioned here, so I'll use that as an example, but Rust could just add a language field to Cargo.toml next to edition that defaults to English (which is what Rust currently uses), and that wouldn't even need a new edition as far as I'm aware. C# could do a field in the csproj file, C and C++ can use compiler flags, and so on.