Problem solved
in my views/fruit.html.haml
instead of
= I18n.t('views.fruits.apple')
it should be
= I18n.t('fruits.apple')
since all the sub-folders are preload from
config/application.rb
config.i18n.load_path += Dir["#{Rails.root.to_s}/config/locales/**/*.{rb,yml}"]
And don't forget you need to restart your server !!