diff --git a/app/controllers/help_controller.rb b/app/controllers/help_controller.rb
index 766781afe..49a5be8d7 100644
--- a/app/controllers/help_controller.rb
+++ b/app/controllers/help_controller.rb
@@ -21,7 +21,7 @@ class HelpController < ApplicationController
   def show_wiki_syntax
     type = params[:type].nil? ? "" : "#{params[:type]}_"
 
-    lang = current_language.to_s
+    lang = current_language.to_s.downcase
     template = "help/wiki_syntax/#{Setting.text_formatting}/#{lang}/wiki_syntax_#{type}#{Setting.text_formatting}"
     unless lookup_context.exists?(template)
       lang = "en"
diff --git a/test/functional/help_controller_test.rb b/test/functional/help_controller_test.rb
index c91cc4bda..0aeaba5da 100644
--- a/test/functional/help_controller_test.rb
+++ b/test/functional/help_controller_test.rb
@@ -66,13 +66,30 @@ class HelpControllerTest < Redmine::ControllerTest
     assert_select 'h1', :text => "Wiki Syntax Schnellreferenz (CommonMark Markdown (GitHub Flavored))"
   end
 
+  def test_get_help_wiki_syntax_should_use_lowercase_region_locale_directory
+    user = User.find(2)
+    user.language = 'ta-IN'
+    user.save!
+    @request.session[:user_id] = 2
+
+    # The Tamil CommonMark help is stored under the lowercase ta-in directory, not ta-IN.
+    with_settings :text_formatting => 'common_mark' do
+      get :show_wiki_syntax
+    end
+    assert_response :success
+
+    assert_select 'h1', :text => "விக்கி தொடரியல் விரைவு குறிப்பு (CommonMark Markdown (GitHub Flavored))"
+  end
+
   def test_get_help_wiki_syntax_should_fallback_to_english
     user = User.find(2)
     user.language = 'ro'
     user.save!
     @request.session[:user_id] = 2
 
-    get :show_wiki_syntax
+    with_settings :text_formatting => 'common_mark' do
+      get :show_wiki_syntax
+    end
     assert_response :success
 
     assert_select 'h1', :text => "Wiki Syntax Quick Reference (CommonMark Markdown (GitHub Flavored))"