diff --git a/lib/redmine/wiki_formatting/common_mark/sanitization_filter.rb b/lib/redmine/wiki_formatting/common_mark/sanitization_filter.rb
index 98a049070..b2125981b 100644
--- a/lib/redmine/wiki_formatting/common_mark/sanitization_filter.rb
+++ b/lib/redmine/wiki_formatting/common_mark/sanitization_filter.rb
@@ -44,7 +44,7 @@ module Redmine
             node = env[:node]
             return unless node.name == "code"
             return unless node.has_attribute?("class")
-            unless node["class"] =~ /\Alanguage-(\w+)\z/
+            unless node["class"] =~ /\Alanguage-(\S+)\z/
               node.remove_attribute("class")
             end
           }
diff --git a/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter.rb b/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter.rb
index 3f46f466b..1f8d8b86f 100644
--- a/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter.rb
+++ b/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter.rb
@@ -28,19 +28,21 @@ module Redmine
         def call
           doc.search("pre > code").each do |node|
             next unless lang = node["class"].presence
-            next unless lang =~ /\Alanguage-(\w+)\z/
+            next unless lang =~ /\Alanguage-(\S+)\z/
 
             lang = $1
             text = node.inner_text
 
+            # original language for extension development
+            node["data-language"] = lang unless node["data-language"]
+
             if Redmine::SyntaxHighlighting.language_supported?(lang)
               html = Redmine::SyntaxHighlighting.highlight_by_language(text, lang)
               next if html.nil?
               node.inner_html = html
               node["class"] = "#{lang} syntaxhl"
             else
-              # unsupported language, strip out the code tag
-              node.parent.inner_html = text
+              node.remove_attribute("class")
             end
           end
           doc
diff --git a/test/unit/lib/redmine/wiki_formatting/common_mark/formatter_test.rb b/test/unit/lib/redmine/wiki_formatting/common_mark/formatter_test.rb
index 6ef7f9d14..70896c1da 100644
--- a/test/unit/lib/redmine/wiki_formatting/common_mark/formatter_test.rb
+++ b/test/unit/lib/redmine/wiki_formatting/common_mark/formatter_test.rb
@@ -94,24 +94,34 @@ class Redmine::WikiFormatting::CommonMark::FormatterTest < ActionView::TestCase
   end
 
   def test_should_support_syntax_highlight
-    text = <<-STR
-~~~ruby
-def foo
-end
-~~~
-STR
+    text = <<~STR
+      ~~~ruby
+      def foo
+      end
+      ~~~
+    STR
     assert_select_in format(text), 'pre code.ruby.syntaxhl' do
       assert_select 'span.k', :text => 'def'
+      assert_select "[data-language='ruby']"
     end
   end
 
   def test_should_not_allow_invalid_language_for_code_blocks
-    text = <<-STR
-~~~foo
-test
-~~~
-STR
-    assert_equal "<pre>test\n</pre>", format(text)
+    text = <<~STR
+      ~~~foo
+      test
+      ~~~
+    STR
+    assert_equal "<pre><code data-language=\"foo\">test\n</code></pre>", format(text)
+  end
+
+  def test_should_preserve_code_block_language_in_data_language
+    text = <<~STR
+      ~~~c-k&r
+      test
+      ~~~
+    STR
+    assert_equal "<pre><code data-language=\"c-k&amp;r\">test\n</code></pre>", format(text)
   end
 
   def test_external_links_should_have_external_css_class
@@ -125,29 +135,29 @@ STR
   end
 
   def test_markdown_should_not_require_surrounded_empty_line
-    text = <<-STR
-This is a list:
-* One
-* Two
-STR
+    text = <<~STR
+      This is a list:
+      * One
+      * Two
+    STR
     assert_equal "<p>This is a list:</p>\n<ul>\n<li>One</li>\n<li>Two</li>\n</ul>", format(text)
   end
 
   def test_footnotes
-    text = <<-STR
-This is some text[^1].
-
-[^1]: This is the foot note
-STR
-
-    expected = <<-EXPECTED
-<p>This is some text<sup><a href="#fn1" id="fnref1">1</a></sup>.</p>
- <ol>
-<li id="fn1">
-<p>This is the foot note <a href="#fnref1">↩</a></p>
-</li>
-</ol> 
-EXPECTED
+    text = <<~STR
+      This is some text[^1].
+
+      [^1]: This is the foot note
+    STR
+
+    expected = <<~EXPECTED
+      <p>This is some text<sup><a href="#fn1" id="fnref1">1</a></sup>.</p>
+       <ol>
+      <li id="fn1">
+      <p>This is the foot note <a href="#fnref1">↩</a></p>
+      </li>
+      </ol> 
+    EXPECTED
 
     assert_equal expected.gsub(%r{[\r\n\t]}, ''), format(text).gsub(%r{[\r\n\t]}, '')
   end
diff --git a/test/unit/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter_test.rb b/test/unit/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter_test.rb
index 2ead13972..45cd79e17 100644
--- a/test/unit/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter_test.rb
+++ b/test/unit/lib/redmine/wiki_formatting/common_mark/syntax_highlight_filter_test.rb
@@ -22,7 +22,7 @@ end
 </code></pre>
     HTML
     expected = <<-HTML
-<pre><code class="ruby syntaxhl">
+<pre><code class="ruby syntaxhl" data-language="ruby">
 <span class="k">def</span> <span class="nf">foo</span>
 <span class="k">end</span>
 </code></pre>
@@ -30,7 +30,7 @@ end
     assert_equal expected, filter(input)
   end
 
-  def test_should_strip_code_for_unknown_lang
+  def test_should_strip_code_class_for_unknown_lang
     input = <<-HTML
 <pre><code class="language-foobar">
 def foo
@@ -38,10 +38,24 @@ end
 </code></pre>
     HTML
     expected = <<-HTML
-<pre>
+<pre><code data-language="foobar">
 def foo
 end
-</pre>
+</code></pre>
+    HTML
+    assert_equal expected, filter(input)
+  end
+
+  def test_should_preserve_lang_in_data_language_attribute
+    input = <<-HTML
+<pre><code class="language-c-k&amp;r">
+int i;
+</code></pre>
+    HTML
+    expected = <<-HTML
+<pre><code data-language="c-k&amp;r">
+int i;
+</code></pre>
     HTML
     assert_equal expected, filter(input)
   end