Use English in Rails admin even though you're using a different default locale for the app.

application.rb

...

    # Use Swedish as default locale.
    config.i18n.default_locale = :sv

...

application_controller.rb

class ApplicationController < ActionController::Base

  ...

  before_filter do|c|
    I18n.locale = c.request.path =~ /admin/ ? :en : I18n.default_locale
  end
  
  ...
  
end