Now we two possible ways to add the tracking code to each external link. The first one is to hack the MediaWiki internal parser for wiki code to generate additional code for each link. While this way will probably work the best it’s pretty complicated and not straightforward. The other way, which is the one will follow, is to use a small JavaScript snippet which will will iterate through the links in every page and add an “onClick” attribute to them with the tracking code.

<script>
var links = document.getElementsByTagName("a");
 
for (var i = 0; i < links.length; i++) {
        if (links[i].className=="external text") {
                addtrackcode(links[i]);
        }
}
 
function addtrackcode(obj) {
        obj.setAttribute('onClick',"javascript:urchinTracker('/outgoing/"+ obj.href.split("://")[1]+"');");
}
</script>

This code snippet should go between you Google Analytics code and the </body> tag, meaning you can add it to /wiki/skins/monobook.php if you haven’t changed the default skin for your MediaWiki. After the code is in place it may take up to 48 hours (usually you don’t have to wait at all) for the external links statistics to show up in the Google Analytics. In the Google Analytics the statistics for clicking on an external link which leads to http://www.google.com will show up as view of the page /outgoing/www.google.com. This script will also track download statistics of files which are linked from the wiki pages (like pdf’’s and such).

While this code does the job, it has a drawbacks. It only tracks the external links created by wiki code (e.g. [http://example.com]) as it uses CSS classes to determine what is external link. However this drawback isn’t very important and overall the script does a decent job tracking the external links in MediaWiki using Google Analytics.

<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
_uacct="UA-xxxx-x";
urchinTracker();
</script>

in every page, preferably just above the </body> tag. The best way to do so will be to put the tracking code inside the base skin php file. That means that unless you changed the default skin for MediaWiki you need to edit /wiki/skins/MonoBook.php. In this file you will find the </body> tag towards the bottom of the file. Insert the tracking code just above it, save the file, and you’re done, as all pages will now show the script. Google Analytics will start gathering statistics usually in about 24-28 hours.

Update:
If you also want to track external links to files and other websites take a look at
Tracking Mediawiki External Links Statistics Using Google Analytics.