WordPress 4.0 language/translation not loading
If you installed WordPress 4.0 and your local language/translation is no longer loading it’s strings for your themes and/or plugins, don’t panic, there is a quick solution!
WordPress 4.0 introduced the “Site Language” setting under “Settings” in the WordPress dashboard which will show a drop down with the available languages.
WPLANG constant in your
wp-config.php file is no longer needed and ineffective. If you have
WPLANG defined in your
wp-config.php file, you will also see a notice below the “Site Language” setting regarding this:
Note: The WPLANG constant in your wp-config.php file is no longer needed.
So just go to “Settings” and site your WordPress installation language there and it will work again.