sorry, forgot to mention. I was talking about the downloadable packages from here in Kentico devnet site.
I was looking for the spanish one and it says: Compatible with 5.5R2 and since I need one compatible with v8, that's why I was looking for some documentation for v8.
However, I think I just found it under: /CMSResources folder I just copied the file CMS.resx and renamed it to CMS.es-mx.resx, this solved my issue when I was in localization and selected culture: Spanish - Mexico.
Thanks in advance