event.rb

#app/models/event.rb

class Event < ActiveRecord::Base
  translates :title, :description
  has_many :event_translations
  accepts_nested_attributes_for :event_translations, :allow_destroy => true

end

event_translation.rb

#app/models/event_translation.rb

class EventTranslation < ActiveRecord::Base
  belongs_to :event
  validates_uniqueness_of :locale, :scope => :event_id
end

events.rb

#app/admin/events.rb


ActiveAdmin.register Event do

  index do
    column :title
    column :description
    default_actions
  end

  filter :title
  filter :description
  filter :date

  form do |f|
    f.inputs "Evento" do
      f.input :date, :as => :datepicker
      f.input :show_date, :as => :datepicker
    end

    f.inputs "Traducciones" do
      f.has_many :event_translations do |g|
        g.input :locale, :as => :radio, :collection => LANGUAGES
        g.input :title
        g.input :description, :as => :string
      end
    end
    f.buttons
  end

end