Fix Translatable when field values are changed to blank

If we ignore all params that are blank, there is no way to
"remove" an attribute (i.e. change its value to blank)

On the other hand, we don't want to create new translations
where all fields are empty, so the new code keeps only the
blank fields which belong to existing translations.

app/controllers/concerns/translatable.rb

@@ -8,12 +8,15 @@ module Translatable
   private
 
     def translation_params(params)
-      resource_model.globalize_attribute_names.select { |k, v| params.include?(k.to_sym) && params[k].present? }
+      resource_model
+        .globalize_attribute_names
+        .select { |k| params[k].present? ||
+                      resource_model.translated_locales.include?(get_locale_from_attribute(k)) }
     end
 
     def delete_translations
-      locales = resource_model.globalize_locales.
+      locales = resource_model.translated_locales
-      select { |k, v| params[:delete_translations].include?(k.to_sym) && params[:delete_translations][k] == "1" }
+                              .select { |l| params.dig(:delete_translations, l) == "1" }
       locales.each do |l|
         Globalize.with_locale(l) do
           resource.translation.destroy
@@ -21,4 +24,8 @@ module Translatable
       end
     end
 
+    def get_locale_from_attribute(attribute_name)
+      locales = resource_model.globalize_locales
+      attribute_name.to_s.match(/(#{locales.join('|')})\Z/)&.captures&.first
+    end
 end

spec/features/translations_spec.rb

@@ -71,6 +71,18 @@ feature "Translations" do
       expect(page).not_to have_link "Español"
     end
 
+    scenario 'Change value of a translated field to blank' do
+      milestone.update_attributes!(status: create(:budget_investment_status))
+      visit @edit_milestone_url
+
+      fill_in 'budget_investment_milestone_description_en', with: ''
+
+      click_button "Update milestone"
+      expect(page).to have_content "Milestone updated successfully"
+
+      expect(milestone.reload.description).to be_blank
+    end
+
     context "Globalize javascript interface" do
 
       scenario "Highlight current locale", :js do