COMPLETELY FREE translated into Spanish Compendium of Essential Reading for Sign Language Interpreters!

http://www.interpretereducation.org/specialization/aslspanishenglish/ then click the ASL/Spanish/English Resources tab

On that page you will also find:

Toward Effective Practice: Interpreting in Spanish-Influenced Settings

and

Hacia Las Prácticas Efectivas: Interpretación en Situaciones Influenciadas por el Español