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
- Fix some locale keys being out of alphabetical order

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

app/helpers/locale_helper.rb

@@ -2,4 +2,34 @@ module LocaleHelper
   def lang_attribute(locale)
     "lang=#{locale}" unless I18n.default_locale.to_s == locale.to_s
   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
+
+  def page_text_direction
+    I18n.t("i18n.direction", locale: I18n.locale, default: "ltr")
+  end
 end

app/models/content_item.rb

@@ -17,6 +17,12 @@ def initialize(content_store_response)
   delegate :to_h, to: :content_store_response
   delegate :cache_control, to: :content_store_response
 
+  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

@@ -103,6 +103,15 @@ cy:
   components:
     figure:
       image_credit: 'Delwedd gan: %{credit}'
+  content_item:
+    schema_name:
+      take_part:
+        few:
+        many:
+        one: Cymryd rhan
+        other: Cymryd rhan
+        two:
+        zero:
   continue: Parhau
   cookies:
     always_on: Mae angen iddynt fod ymlaen bob amser.
@@ -812,6 +821,11 @@ cy:
       uk_bank_holidays:
       universal_credit:
     most_active:
+  i18n:
+    direction: ltr
+  language_names:
+    cy: Cymraeg
+    en:
   'no': Na
   or:
   place:
@@ -874,8 +888,8 @@ cy:
       description:
       title:
       body:
-    start_title: 
-    start_notes: 
-    end_title:   
-    end_notes: 
+    start_title:
+    start_notes:
+    end_title:
+    end_notes:
   'yes': Ie

config/locales/en.yml

@@ -103,6 +103,11 @@ en:
   components:
     figure:
       image_credit: 'Image credit: %{credit}'
+  content_item:
+    schema_name:
+      take_part:
+        one: Take part
+        other: Take part
   continue: Continue
   cookies:
     always_on: They always need to be on.
@@ -650,6 +655,11 @@ en:
         link: /vehicle-tax
       - title: VAT rates
         link: /vat-rates
+  i18n:
+    direction: ltr
+  language_names:
+    cy: Welsh
+    en: English
   'no': 'No'
   or: or
   place: