Welcome Manuel!
I have added you to the translation group (which at this point means you can edit ALL languages so try to stick to the ones you know 😉.
You can add the gl_ES locale using the acs-lang admin interface:
http://translate.dotlrn.collaboraid.net/acs-lang/admin/
There is a "getting started" guide at the bottom of the index page:
http://translate.dotlrn.collaboraid.net/
If you have any questions you can post them here.
Happy translating!