diff --git a/.circleci/config.yml b/.circleci/config.yml
index f764cb611..59702c139 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -144,7 +144,7 @@ jobs:
   # Backend tests with parallelization
   backend-tests:
     <<: *defaults
-    parallelism: 20
+    parallelism: 18
     steps:
       - checkout
       - node/install:
diff --git a/app/controllers/concerns/portal_home_data.rb b/app/controllers/concerns/portal_home_data.rb
new file mode 100644
index 000000000..633071301
--- /dev/null
+++ b/app/controllers/concerns/portal_home_data.rb
@@ -0,0 +1,29 @@
+module PortalHomeData
+  extend ActiveSupport::Concern
+
+  private
+
+  def load_home_data
+    base_articles = @portal.articles.published.where(locale: @locale).includes(:author, :category)
+    @visible_categories = @portal.categories
+                                 .where(locale: @locale)
+                                 .joins(:articles).where(articles: { status: :published })
+                                 .order(position: :asc)
+                                 .group('categories.id')
+    @popular_topics = @visible_categories.first(3)
+    @featured = base_articles.order_by_views.limit(6)
+    @category_contributors = build_category_contributors(@visible_categories)
+  end
+
+  def build_category_contributors(categories)
+    category_ids = categories.map(&:id)
+    return {} if category_ids.empty?
+
+    @portal.articles
+           .published
+           .where(locale: @locale, category_id: category_ids)
+           .includes(:author)
+           .group_by(&:category_id)
+           .transform_values { |articles| articles.filter_map(&:author).uniq.first(3) }
+  end
+end
diff --git a/app/controllers/dashboard_controller.rb b/app/controllers/dashboard_controller.rb
index b6df015f7..a369830b6 100644
--- a/app/controllers/dashboard_controller.rb
+++ b/app/controllers/dashboard_controller.rb
@@ -1,5 +1,6 @@
 class DashboardController < ActionController::Base
   include SwitchLocale
+  include PortalHomeData
 
   GLOBAL_CONFIG_KEYS = %w[
     LOGO
@@ -63,6 +64,10 @@ class DashboardController < ActionController::Base
     return unless @portal
 
     @locale = @portal.default_locale
+    if @portal.layout == 'documentation'
+      request.variant = :documentation
+      load_home_data
+    end
     render 'public/api/v1/portals/show', layout: 'portal', portal: @portal and return
   end
 
diff --git a/app/controllers/public/api/v1/portals/base_controller.rb b/app/controllers/public/api/v1/portals/base_controller.rb
index 2991b84d2..323440304 100644
--- a/app/controllers/public/api/v1/portals/base_controller.rb
+++ b/app/controllers/public/api/v1/portals/base_controller.rb
@@ -39,9 +39,11 @@ class Public::Api::V1::Portals::BaseController < PublicController
   end
 
   def switch_locale_with_portal(&)
-    @locale = validate_and_get_locale(params[:locale])
+    # Keep @locale as the portal's own locale code (e.g. th_TH) for content queries,
+    # while UI translations fall back to an available I18n locale (e.g. th).
+    @locale = params[:locale]
 
-    I18n.with_locale(@locale, &)
+    I18n.with_locale(validate_and_get_locale(@locale), &)
   end
 
   def switch_locale_with_article(&)
@@ -49,13 +51,12 @@ class Public::Api::V1::Portals::BaseController < PublicController
     Rails.logger.info "Article: not found for slug: #{params[:article_slug]}"
     render_404 && return if article.blank?
 
-    article_locale = if article.category.present?
-                       article.category.locale
-                     else
-                       article.locale
-                     end
-    @locale = validate_and_get_locale(article_locale)
-    I18n.with_locale(@locale, &)
+    @locale = if article.category.present?
+                article.category.locale
+              else
+                article.locale
+              end
+    I18n.with_locale(validate_and_get_locale(@locale), &)
   end
 
   def allow_iframe_requests
diff --git a/app/controllers/public/api/v1/portals_controller.rb b/app/controllers/public/api/v1/portals_controller.rb
index 57db11aec..4982278d7 100644
--- a/app/controllers/public/api/v1/portals_controller.rb
+++ b/app/controllers/public/api/v1/portals_controller.rb
@@ -1,4 +1,6 @@
 class Public::Api::V1::PortalsController < Public::Api::V1::Portals::BaseController
+  include PortalHomeData
+
   before_action :ensure_custom_domain_request, only: [:show]
   before_action :redirect_to_portal_with_locale, only: [:show]
   before_action :portal
@@ -31,28 +33,4 @@ class Public::Api::V1::PortalsController < Public::Api::V1::Portals::BaseControl
     portal
     redirect_to "/hc/#{@portal.slug}/#{@portal.default_locale}"
   end
-
-  def load_home_data
-    base_articles = @portal.articles.published.where(locale: @locale).includes(:author, :category)
-    @visible_categories = @portal.categories
-                                 .where(locale: @locale)
-                                 .joins(:articles).where(articles: { status: :published })
-                                 .order(position: :asc)
-                                 .group('categories.id')
-    @popular_topics = @visible_categories.first(3)
-    @featured = base_articles.order_by_views.limit(6)
-    @category_contributors = build_category_contributors(@visible_categories)
-  end
-
-  def build_category_contributors(categories)
-    category_ids = categories.map(&:id)
-    return {} if category_ids.empty?
-
-    @portal.articles
-           .published
-           .where(locale: @locale, category_id: category_ids)
-           .includes(:author)
-           .group_by(&:category_id)
-           .transform_values { |articles| articles.filter_map(&:author).uniq.first(3) }
-  end
 end
diff --git a/spec/controllers/dashboard_custom_domain_spec.rb b/spec/controllers/dashboard_custom_domain_spec.rb
new file mode 100644
index 000000000..4d791defb
--- /dev/null
+++ b/spec/controllers/dashboard_custom_domain_spec.rb
@@ -0,0 +1,50 @@
+require 'rails_helper'
+
+describe 'GET / on a help center custom domain', type: :request do
+  let(:account) { create(:account) }
+  let(:agent) { create(:user, account: account, role: :agent) }
+
+  around do |example|
+    with_modified_env FRONTEND_URL: 'http://www.chatwoot.test' do
+      example.run
+    end
+  end
+
+  context 'when the portal uses the documentation layout' do
+    let!(:portal) do
+      create(:portal, account: account, slug: 'doc-portal', custom_domain: 'docs.example.com',
+                      config: { allowed_locales: ['en'], default_locale: 'en', layout: 'documentation' })
+    end
+    let!(:category) do
+      create(:category, name: 'Getting Started', portal: portal, account_id: account.id, locale: 'en', slug: 'getting-started')
+    end
+
+    before do
+      create(:article, category: category, portal: portal, account: account, author: agent, locale: 'en', status: :published)
+    end
+
+    it 'renders the documentation home in place without redirecting' do
+      host! portal.custom_domain
+      get '/'
+
+      expect(response).to have_http_status(:success)
+      expect(response.body).to include('sidebar-drawer-checkbox')
+      expect(response.body).to include('Getting Started')
+    end
+  end
+
+  context 'when the portal uses the classic layout' do
+    let!(:portal) do
+      create(:portal, account: account, slug: 'classic-portal', custom_domain: 'classic.example.com',
+                      config: { allowed_locales: ['en'], default_locale: 'en', layout: 'classic' })
+    end
+
+    it 'renders the classic home without the documentation layout' do
+      host! portal.custom_domain
+      get '/'
+
+      expect(response).to have_http_status(:success)
+      expect(response.body).not_to include('sidebar-drawer-checkbox')
+    end
+  end
+end
diff --git a/spec/controllers/public/api/v1/portals/articles_controller_spec.rb b/spec/controllers/public/api/v1/portals/articles_controller_spec.rb
index 8bebd3b9d..89d9de6b4 100644
--- a/spec/controllers/public/api/v1/portals/articles_controller_spec.rb
+++ b/spec/controllers/public/api/v1/portals/articles_controller_spec.rb
@@ -211,4 +211,30 @@ RSpec.describe 'Public Articles API', type: :request do
       expect(response.headers['Content-Type']).to eq('image/png')
     end
   end
+
+  describe 'documentation layout sidebar for a region-variant locale' do
+    let!(:th_portal) do
+      create(:portal, slug: 'th-portal', custom_domain: 'th.example.com',
+                      config: { allowed_locales: ['th_TH'], default_locale: 'th_TH', layout: 'documentation' })
+    end
+    let!(:th_category) do
+      create(:category, name: 'TH Category', portal: th_portal, account_id: account.id, locale: 'th_TH', slug: 'th-cat')
+    end
+    let!(:th_article) do
+      create(:article, category: th_category, portal: th_portal, account_id: account.id, author_id: agent.id, locale: 'th_TH')
+    end
+
+    before do
+      create(:article, category: th_category, portal: th_portal, account_id: account.id, author_id: agent.id,
+                       locale: 'th_TH', title: 'Sibling In Sidebar', status: :published)
+    end
+
+    it 'lists the category and sibling articles using the full portal locale' do
+      host! 'th.example.com'
+      get "/hc/#{th_portal.slug}/articles/#{th_article.slug}"
+
+      expect(response).to have_http_status(:success)
+      expect(response.body).to include('Sibling In Sidebar')
+    end
+  end
 end