Fatal error: Cannot declare class WP_Widget, because the name is already in use in /var/www/Adace/wp-includes/class-wp-widget.php on line 21

Fatal error: Uncaught Error: Call to a member function set() on null in /var/www/Adace/wp-includes/l10n.php:786 Stack trace: #0 /var/www/Adace/wp-includes/l10n.php(874): load_textdomain() #1 /var/www/Adace/wp-includes/class-wp-fatal-error-handler.php(47): load_default_textdomain() #2 [internal function]: WP_Fatal_Error_Handler->handle() #3 {main} thrown in /var/www/Adace/wp-includes/l10n.php on line 786