FEATURE: default_code_lang for syntax highlighting is configurable

app/assets/javascripts/discourse/dialects/github_code_dialect.js

@@ -19,7 +19,7 @@ Discourse.Dialect.replaceBlock({
   stop: '```',
   emitter: function(blockContents, matches) {
 
-    var klass = 'lang-auto';
+    var klass = Discourse.SiteSettings.default_code_lang;
     if (matches[1] && acceptableCodeClasses.indexOf(matches[1]) !== -1) {
       klass = matches[1];
     }

config/locales/server.en.yml

@@ -738,6 +738,7 @@ en:
     display_name_on_posts: "Also show a user's full name on their posts"
     invites_shown: "Maximum invites shown on a user page"
     short_progress_text_threshold: "After the number of posts in a topic goes above this number, the progress bar will only show the current post number. If you change the progress bar's width, you may need to change this value."
+    default_code_lang: "Default programming language syntax highlighting applied to GitHub code blocks (lang-auto, ruby, python etc.)"
 
   notification_types:
     mentioned: "%{display_username} mentioned you in %{link}"

config/site_settings.yml

@@ -200,6 +200,9 @@ posting:
   short_progress_text_threshold:
     client: true
     default: 1000
+  default_code_lang:
+    client: true
+    default: "lang-auto"
 
 email:
   email_time_window_mins: 10