Fix updating translatables without current locale

The current locale wasn't being marked for destruction and so saving
the record tried to create a new translation for the current locale.

app/helpers/translatable_form_helper.rb

@@ -39,7 +39,9 @@ module TranslatableFormHelper
 
       def new_translation_for(locale)
         @object.translations.new(locale: locale).tap do |translation|
-          translation.mark_for_destruction unless locale == I18n.locale
+          unless locale == I18n.locale && no_other_translations?(translation)
+            translation.mark_for_destruction
+          end
         end
       end
 
@@ -50,6 +52,10 @@ module TranslatableFormHelper
           data:  { locale: locale }
         }
       end
+
+      def no_other_translations?(translation)
+        (@object.translations - [translation]).reject(&:_destroy).empty?
+      end
   end
 
   class TranslationsFieldsBuilder < FoundationRailsHelper::FormBuilder

spec/shared/features/translatable.rb

@@ -119,6 +119,29 @@ shared_examples "translatable" do |factory_name, path_name, input_fields, textar
       expect_page_to_have_translatable_field field, :es, with: ""
     end
 
+    scenario "Update a translation not having the current locale", :js do
+      translatable.translations.destroy_all
+
+      translatable.translations.create(
+        fields.map { |field| [field, text_for(field, :fr)] }.to_h.merge(locale: :fr)
+      )
+
+      visit path
+
+      expect(page).not_to have_link "English"
+      expect(page).to have_link "Français"
+
+      click_button update_button_text
+
+      expect(page).not_to have_css "#error_explanation"
+      expect(page).not_to have_link "English"
+
+      visit path
+
+      expect(page).not_to have_link "English"
+      expect(page).to have_link "Français"
+    end
+
     scenario "Remove a translation", :js do
       visit path