What is the best end-user language for data transformation (ETL), ideally something that can run in a JVM (with a LGPL like license).
With end-user meaning users who are IT related but might not be experts in OO or like.
You can try CloverETL. It is Java based ETL tool. You can either define transformation through its visual designer or handcode directly in XML files that are used to store data about transformations.
It also uses its own transformation language - CTL that is used inside transformation components. You do not need to be expert in OOP to use it.