implement translation behavior default locale

Unless explicitly overriden, the behavior now reads I18n::defaultLocale() to find the locale to return translations in.

Bundled with this change set is adding support to the translate behavior
for unhydrated result sets

Closes #4509

Ref #4660 
in the constructor can also be too late - I don't like having en_US in this class, I have an idea how to remove it though.