YAML is all but human-friendly. It has far too many special features and edge cases for most people. Something simple like Java properties files would solve something like markdown front matter perfectly fine.
Look at the documentation [0] or at the OpenJDK code. Both assume ISO-8859-1, unless you're dealing with a special case where resource bundles are involved.
[0]: https://docs.oracle.com/en/java/javase/21/docs/api/java.base...