When you are running a Wordpress based blog and you run across the following error message:

Fatal error: Cannot instantiate non-existent class: cachedfilereader in /some/directory/path/wp-includes/wp-l10n.php on line 72

the cause for this issue is clear - you simply omitted to setup the WPLANG variable in your wp-config.php to a valid locale, but simultaniously you have activated either a localized plugin or theme.

But don’t worry, the solution is near, and your blog isn’t really broken. Just open the wp-config.php with your favorite text editor (even notepad.exe is sufficient) and seek out the following paragraph:

// Change this to localize WordPress.  A corresponding MO file for the
// chosen language must be installed to wp-includes/languages.
// For example, install de.mo to wp-includes/languages and set WPLANG to ‘de’
// to enable German language support.
define (’WPLANG’, ‘’); 

Now set the WPLANG definition to a valid locale, e.g. ‘en_US’ for U.S. english, or ‘es_ES’ for Spanish and so on. Save your change, reupload the wp-config.php to your webserver and re-enter the admin panel of your blog, and everything should be fine again.

Though this is strictly speaking a misconfiguration by the user, it is a very annoying error, and I can’t understand why Wordpress doesn’t fall back to a default locale in case the blog owner omitted to set a locale value.

Thanx to Brian from thecodecave for kicking me ass that this is really an issue for the usual wordpress user