To change Noosfero default change, first you need to generate some translations files:

mkdir tmp
rake noosfero:translations:compile

  After that, edit config/local.rb (or create it if it doesn't exist) and add:

Noosfero.default_locale = 'pt'

This will change the default language to Portuguese. You may change to any of the folder names at locale folder.

-- BraulioBhavamitraBO - 02 Aug 2010