How to fix this “WordPress database error: [Unknown character set: ‘utf8mb4’] ~” error. Simply change “utf8mb4” to “utf8” in the Database Charset setting in your wp-config.php file.
Update (2018.02.01): Do NOT follow any of that above. You’re going to want to keep the ‘utf8mb4’ under Database Charset in your wp-config.php file, but you’ll need to upgrade your WordPress database. You can do so by navigating here YOUR_WP_INSTALL_FOLDER/wp-admin/includes/upgrade.php. For reasons why, read this from WordPress about utf8mb4 being the standard charset for WordPress. And then why you should never use utf8 for WordPress databases, instead utf8mb4.