Fix: Suppress HTML output from async translation updates during core update

features/core-update.feature

@@ -384,3 +384,38 @@ Feature: Update WordPress core
       """
       Success:
       """
+
+  Scenario: No HTML output from async translation updates during core update
+    Given a WP install
+    And an empty cache
+
+    # Using `try` in case there are checksum warnings.
+    When I try `wp core download --version=6.5 --locale=de_DE --force`
+    Then STDOUT should contain:
+      """
+      Success: WordPress downloaded.
+      """
+
+    When I run `wp core version --extra`
+    Then STDOUT should contain:
+      """
+      Package language:  de_DE
+      """
+
+    When I run `wp core update --version=latest --force`
+    Then STDOUT should not contain:
+      """
+      <p>
+      """
+    And STDOUT should not contain:
+      """
+      <div
+      """
+    And STDOUT should not contain:
+      """
+      <script
+      """
+    And STDOUT should not contain:
+      """
+      </div>
+      """

src/Core_Command.php

@@ -1213,6 +1213,15 @@ public function update( $args, $assoc_args ) {
 
 			require_once ABSPATH . 'wp-admin/includes/upgrade.php';
 
+			// Prevent async translation updates which output HTML.
+			add_action(
+				'upgrader_process_complete',
+				static function () {
+					remove_action( 'upgrader_process_complete', array( 'Language_Pack_Upgrader', 'async_upgrade' ), 20 );
+				},
+				1
+			);
+
 			if ( $update->version ) {
 				WP_CLI::log( "Updating to version {$update->version} ({$update->locale})..." );
 			} else {