Is there a standard language/interface for programmatic ETL in SQL Server?
There is a tool that enables this - http://www.varigence.com/products/biml.html

There's a commerical version, but we also include some of the BIML functionality in BIDS Helper, a free tool. http://bidshelper.codeplex.com/

I'm happy to answer any questions that you might have about it.

This is a tool that my company provides.