NEM is built as a JAVA application but uses JSON API's. JSON is not a programming language , it's merely a way to format data similar to XML.
Mijin and NEM API's are fully interchangeable. Noteworthy: Mijin referred the API documentation on bob.nem.ninja to their customers.
In other words any company that was testing Mijin initially ( I don't know about the status now...) used the NEM API as reference!