Add global language switch capabilities to the refdoc

See gh-21778

gradle/docs.gradle

@@ -94,10 +94,10 @@ dependencies {
 
 task extractDocResources(type: Sync) {
 	dependsOn configurations.docs
-	from "src/docs/asciidoc/"
 	from {
 		configurations.docs.collect { zipTree(it) }
 	}
+	from "src/docs/asciidoc/"
 	into "$buildDir/asciidoc/build"
 }
 

src/docs/asciidoc/docinfo-footer.html

@@ -0,0 +1,3 @@
+<script type="text/javascript" src="js/tocbot/tocbot.min.js"></script>
+<script type="text/javascript" src="js/toc.js"></script>
+<script type="text/javascript" src="js/switch-language.js"></script>

src/docs/asciidoc/js/switch-language.js

@@ -0,0 +1,18 @@
+function globalSwitch() {
+    $('.switch--item').each(function() {
+        $(this).off('click');
+        $(this).on('click', function() {
+            selectedText = $(this).text()
+            selectedIndex = $(this).index()
+            $(".switch--item").filter(function() { return ($(this).text() === selectedText) }).each(function() {
+                $(this).addClass('selected');
+                $(this).siblings().removeClass('selected');
+                selectedContent = $(this).parent().siblings(".content").eq(selectedIndex)
+                selectedContent.removeClass('hidden');
+                selectedContent.siblings().addClass('hidden');
+            });
+        });
+    });
+}
+
+$(globalSwitch);