Integrate my systems with FHIR

I am trying to integrate my systems with FHIR in order to be able to accept any query/script that comes in FHIR. How do I set up a module that does a FHIR conversion to my own data language, do I have to have a FHIR server, duplicate the data from my repository but in FHIR and then introduce an ETL that does the FHIR conversion to my own data language?

Thank you very much for everything.

Well, that depends - what you have to do is put up an interface that conforms to the stated public interface - usually, but no necessarily - a RESTful API. What you do behind that API is your choice.