Add translation shared partial

- Add helper to provide language names and translate content info
  into component format
- Add methods to ContentItem to provide available translations

Commit audit trail:
- app/helpers/locale_helper.rb alphagov/government-frontend@90f0dd8
  https://github.com/alphagov/government-frontend/blame/517e4d4619595806bc9a1fb904b2badb65332eaf/app/helpers/application_helper.rb
- app/views/shared/_translations.html.erb alphagov/government-frontend@887399c
- en.yml/cy.yml alphagov/government-frontend@665e1c1

app/helpers/locale_helper.rb

@@ -6,4 +6,30 @@ def lang_attribute(locale)
   def page_text_direction
     I18n.t("i18n.direction", locale: I18n.locale, default: "ltr")
   end
+
+  def native_language_name_for(locale)
+    I18n.t("language_names.#{locale}", locale:)
+  end
+
+  def translations_for_nav(translations)
+    translations.map do |translation|
+      {
+        locale: translation["locale"],
+        base_path: translation["base_path"],
+        text: native_language_name_for(translation["locale"]),
+      }.tap do |h|
+        h[:active] = true if h[:locale] == I18n.locale.to_s
+      end
+    end
+  end
+
+  def t_locale_fallback(key, options = {})
+    options[:locale] = I18n.locale
+    options[:fallback] = nil
+    translation = I18n.t(key, **options)
+
+    if translation.nil? || translation.downcase.include?("translation missing")
+      I18n.default_locale
+    end
+  end
 end

app/models/content_item.rb

@@ -38,6 +38,12 @@ def method_missing(method_name, *_args, &_block)
     end
   end
 
+  def available_translations
+    translations = content_store_response["links"]["available_translations"] || []
+
+    translations.sort_by { |t| t["locale"] == I18n.default_locale.to_s ? "" : t["locale"] }
+  end
+
 private
 
   def ordered_related_items(links)

app/views/shared/_translations.html.erb

@@ -0,0 +1,6 @@
+<% if @content_item.available_translations.any? %>
+  <div class="govuk-grid-column-one-third">
+    <%= render 'govuk_publishing_components/components/translation_nav',
+        translations: translations_for_nav(@content_item.available_translations) %>
+  </div>
+<% end %>

config/locales/cy.yml

@@ -821,7 +821,10 @@ cy:
       universal_credit:
     most_active:
   i18n:
-    direction:
+    direction: ltr
+  language_names:
+    cy: Cymraeg
+    en:
   'no': Na
   or:
   place:

config/locales/en.yml

@@ -639,27 +639,30 @@ en:
       universal_credit: Sign in to your Universal Credit account
     most_active:
     - title: Find a job
-      link: "/find-a-job"
+      link: /find-a-job
     - title: Log in to student finance
-      link: "/student-finance-register-login"
+      link: /student-finance-register-login
     - title: Passport fees
-      link: "/passport-fees"
+      link: /passport-fees
     - title: Jobseeker's Allowance
-      link: "/jobseekers-allowance"
+      link: /jobseekers-allowance
     - title: Council Tax bands
-      link: "/council-tax-bands"
+      link: /council-tax-bands
     - title: Running a limited company
-      link: "/running-a-limited-company"
+      link: /running-a-limited-company
     - title: Driving theory test
-      link: "/book-theory-test"
+      link: /book-theory-test
     - title: Vehicle tax rates
-      link: "/calculate-tax-rates-for-new-cars"
+      link: /calculate-tax-rates-for-new-cars
     - title: Renew vehicle tax
-      link: "/vehicle-tax"
+      link: /vehicle-tax
     - title: VAT rates
-      link: "/vat-rates"
+      link: /vat-rates
   i18n:
     direction: ltr
+  language_names:
+    cy: Welsh
+    en: English
   'no': 'No'
   or: or
   place: