I want to change the newsletter title: "sign up for our newsletter" on the footer to a different language but I want to keep the original english one, but I can't find anything in static block...which file or block should I edit?
If you want to change the translation only, you need to look at
/Your_Package/app/locale/en_US/Mage_Newsletter.csv
en_US = English for US, en_BR = English for UK and so on.
The title Sign Up for Our Newsletter is not in the XML file but in the PHTML and it's located at
/Your_Package/app/design/frontend/Your_Theme/default/template/newsletter/subscribe.phtml