Fatal error: Cannot declare class WP_Block_Parser_Block, because the name is already in use in /wp-includes/class-wp-block-parser.php on line 15

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