¿Someone want to help translate the Framewoek to spanish at codeigniter.es?

Is possible to translate it on my language and add some customizations to the site?

For example, add an extra menu "Find a developer" or something like.

You *could* do that, but you would want to make sure that any such changes are clearly NOT part of the user guide.
You would not want to give the impression that the project endorses specific developers, and that such endorsement is built into the user guide.

You could make a regional group site, part of which is the user guide (translated), and part of which is clearly region-specific, and created/maintained by people in that region.