Add internationalization (i18n) support for PHPMailer error messages

src/wp-includes/class-wp-phpmailer.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * PHPMailer extensions for WordPress
+ *
+ * @package WordPress
+ * @since 6.7.1
+ */
+
+/**
+ * PHPMailer child class
+ *
+ * Overrides the internationalization method in order to use WordPress' instead.
+ *
+ * @since 6.7.1
+ */
+class WP_PHPMailer extends PHPMailer\PHPMailer\PHPMailer {
+	/**
+	 * Public constructor
+	 *
+	 * @param bool $exceptions Whether to throw exceptions for errors.
+	 */
+	public function __construct( $exceptions = false ) {
+		parent::__construct( $exceptions );
+		$this->SetLanguage();
+	}
+
+	/**
+	 * Defines the error messages using WordPress' internationalization method.
+	 *
+	 * @return bool Always returns true in order to mimic PHPMailer's setLanguage() behavior
+	 */
+	public function SetLanguage( $langcode = 'en', $lang_path = '' ) {
+		$error_strings  = array(
+			'authenticate'         => __( 'SMTP Error: Could not authenticate.' ),
+			'buggy_php'            => __(
+				'Your version of PHP is affected by a bug that may result in corrupted messages. To fix it, switch to sending using SMTP, disable the mail.add_x_header option in your php.ini, switch to MacOS or Linux, or upgrade your PHP to version 7.0.17+ or 7.1.3+.'
+			),
+			'connect_host'         => __( 'SMTP Error: Could not connect to SMTP host.' ),
+			'data_not_accepted'    => __( 'SMTP Error: data not accepted.' ),
+			'empty_message'        => __( 'Message body empty' ),
+			'encoding'             => __( 'Unknown encoding: ' ),
+			'execute'              => __( 'Could not execute: ' ),
+			'extension_missing'    => __( 'Extension missing: ' ),
+			'file_access'          => __( 'Could not access file: ' ),
+			'file_open'            => __( 'File Error: Could not open file: ' ),
+			'from_failed'          => __( 'The following From address failed: ' ),
+			'instantiate'          => __( 'Could not instantiate mail function.' ),
+			'invalid_address'      => __( 'Invalid address: ' ),
+			'invalid_header'       => __( 'Invalid header name or value' ),
+			'invalid_hostentry'    => __( 'Invalid hostentry: ' ),
+			'invalid_host'         => __( 'Invalid host: ' ),
+			'mailer_not_supported' => __( ' mailer is not supported.' ),
+			'provide_address'      => __( 'You must provide at least one recipient email address.' ),
+			'recipients_failed'    => __( 'SMTP Error: The following recipients failed: ' ),
+			'signing'              => __( 'Signing Error: ' ),
+			'smtp_code'            => __( 'SMTP code: ' ),
+			'smtp_code_ex'         => __( 'Additional SMTP info: ' ),
+			'smtp_connect_failed'  => __( 'SMTP connect() failed.' ),
+			'smtp_detail'          => __( 'Detail: ' ),
+			'smtp_error'           => __( 'SMTP server error: ' ),
+			'variable_set'         => __( 'Cannot set or reset variable: ' ),
+		);
+		$this->language = $error_strings;
+		return true;
+	}
+}

src/wp-includes/pluggable.php

@@ -251,7 +251,8 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 			require_once ABSPATH . WPINC . '/PHPMailer/PHPMailer.php';
 			require_once ABSPATH . WPINC . '/PHPMailer/SMTP.php';
 			require_once ABSPATH . WPINC . '/PHPMailer/Exception.php';
-			$phpmailer = new PHPMailer\PHPMailer\PHPMailer( true );
+			require_once ABSPATH . WPINC . '/class-wp-phpmailer.php';
+			$phpmailer = new WP_PHPMailer( true );
 
 			$phpmailer::$validator = static function ( $email ) {
 				return (bool) is_email( $email );

tests/phpunit/tests/mail/test-phpmailer-translations.php

@@ -0,0 +1,18 @@
+<?php
+
+class Test_PHPMailer_Translations extends WP_UnitTestCase {
+	/**
+	 * @ticket 23311
+	 */
+	public function test_wp_phpmailer_error_message_keys_match() {
+		require_once ABSPATH . WPINC . '/PHPMailer/PHPMailer.php';
+		require_once ABSPATH . WPINC . '/class-wp-phpmailer.php';
+
+		$phpmailer = new PHPMailer\PHPMailer\PHPMailer();
+		$phpmailer->SetLanguage();
+
+		$wp_phpmailer = new WP_PHPMailer();
+
+		$this->assertTrue( array_keys( $phpmailer->GetTranslations() ) === array_keys( $wp_phpmailer->GetTranslations() ) );
+	}
+}