IRIS and Caché / Ensemble offer the possibility to add Languages Extension as SystemFunctions, SystemVariables, SystemCommands
The related documentation tells you where to add the system-wide extension. Parameter passing is not covered explicitly.
InterSystems ObjectScript is a scripting language to operate with data using any data model of InterSystems Data Platform (Objects, Relational, Key-Value, Document, Globals) and to develop business logic for serverside applications on InterSystems Data Platform.