docs: Update CHANGELOG

Author: BriannaDelgado

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Added new language constants from January 2026 API release of 81 new languages.
+- Added `jsonBody` option to `SendRequestOptions`, enabling JSON-encoded API calls.
 
 ### Changed
 - Updated formality tests to accept either formal or informal output when using default formality,