That’s ok. The codebase changed a lot since that time when most of the code was written by original author, Whales. There were no JSONs, all the stuff was hardcoded. It’s much larger project nowadays.
Kudos for diving into the code and having interest in the project. Such games really benefit from passionate modders like you.
YAML for human-written files, JSON for back-to-front and protobuf for back-to-back. XML is an abomination.