Add validation to check translations amount on updates

In order to not allow users to remove all persited
translations from any resource. A few exceptions were
added:

* Does not apply to globalizable models without
   translatable attributes required
* Make a copy of main model error on current translations to be more realistic

spec/shared/features/edit_translatable.rb

@@ -236,6 +236,19 @@ shared_examples "edit_translatable" do |factory_name, path_name, input_fields, t
       expect_not_to_have_language "Español"
     end
 
+    scenario "Remove all translations should show an error message", :js do
+      skip("can't have invalid translations") if required_fields.empty?
+
+      visit path
+
+      click_link "Remove language"
+      click_link "Remove language"
+
+      click_button update_button_text
+
+      expect(page).to have_content "Is mandatory to provide one translation at least"
+    end
+
     scenario "Remove a translation with invalid data", :js do
       skip("can't have invalid translations") if required_fields.empty?