WordPress 3.3 Fix for “Fatal Error Undefined Function is_rtl()”

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Here’s a quick fix if you’re seeing the following error after upgrading to WordPress 3.3:

Fatal error: Call to undefined function is_rtl() in /wp-includes/general-template.php on line 2102

First of all, don’t panic, the error seems to affect the admin dashboard but not the publicly accessible areas of your site. Secondly, it’s a fairly simple fix.

The cause is most likely a plugin, and for many people reading this it’s the “PopupDomination” plugin.

Fix for “Fatal Error Undefined Function is_rtl()”:

1. Login to your site via FTP and navigate to the /wp-content/plugins directory.
2. If you have PopupDomination installed look at the directory names starting with ‘P’ and see if you can identify it (it could be “popup-domination”, “popupD” or similar).
3. Rename that folder to “PopupDomination-broken” or something similar.
4. You’re done! Reload the page and everything should be working. Contact the plugin author and ask them for a fixed version and re-enable after you’ve updated.

In the unlikely event that didn’t fix your problem, try the following:

• Deactivate all plugins to see if this resolves the problem. If this works, re-activate plugins one by one until you find the problematic plugin(s).
• Try renaming the plugins directory to plugins-broken by FTP (sometimes, an inactive plugin can cause a problem so this works).
• Deactivate plugins in the mu-plugins folder by renaming that directory to mu-plugins-old

You can find more on how to do this on Fixing a Broken WordPress Site

Hope this helps!