Add internationalization (i18n) support for PHPMailer error messages

src/wp-includes/class-wp-locale-switcher.php

@@ -273,18 +273,23 @@ private function load_translations( $locale ) {
 	 * @since 4.7.0
 	 *
 	 * @global WP_Locale $wp_locale WordPress date and time locale object.
+	 * @global PHPMailer\PHPMailer\PHPMailer $phpmailer
 	 *
 	 * @param string $locale The locale to change to.
 	 */
 	private function change_locale( $locale ) {
-		global $wp_locale;
+		global $wp_locale, $phpmailer;
 
 		$this->load_translations( $locale );
 
 		$wp_locale = new WP_Locale();
 
 		WP_Translation_Controller::get_instance()->set_locale( $locale );
 
+		if ( $phpmailer instanceof WP_PHPMailer ) {
+			$phpmailer->SetLanguage();
+		}
+
 		/**
 		 * Fires when the locale is switched to or restored.
 		 *

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

@@ -0,0 +1,92 @@
+<?php
+/**
+ * WordPress PHPMailer class.
+ *
+ * @package WordPress
+ * @since 6.8.0
+ */
+
+/**
+ * WordPress PHPMailer class.
+ *
+ * Overrides the internationalization method in order to use WordPress' instead.
+ *
+ * @since 6.8.0
+ */
+class WP_PHPMailer extends PHPMailer\PHPMailer\PHPMailer {
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 6.8.0
+	 *
+	 * @param bool $exceptions Optional. Whether to throw exceptions for errors. Default false.
+	 */
+	public function __construct( $exceptions = false ) {
+		parent::__construct( $exceptions );
+		$this->SetLanguage();
+	}
+
+	/**
+	 * Defines the error messages using WordPress' internationalization method.
+	 *
+	 * @since 6.8.0
+	 *
+	 * @return true Always returns true.
+	 */
+	public function SetLanguage( $langcode = 'en', $lang_path = '' ) {
+		$error_strings  = array(
+			'authenticate'         => __( 'SMTP Error: Could not authenticate.' ),
+			'buggy_php'            => sprintf(
+				/* translators: 1: mail.add_x_header. 2: php.ini */
+				__(
+					'Your version of PHP is affected by a bug that may result in corrupted messages. To fix it, switch to sending using SMTP, disable the %1$s option in your %2$s, or switch to MacOS or Linux, or upgrade your PHP version.'
+				),
+				'mail.add_x_header',
+				'php.ini'
+			),
+			'connect_host'         => __( 'SMTP Error: Could not connect to SMTP host.' ),
+			'data_not_accepted'    => __( 'SMTP Error: data not accepted.' ),
+			'empty_message'        => __( 'Message body empty' ),
+			/* translators: There is a space after the colon. */
+			'encoding'             => __( 'Unknown encoding: ' ),
+			/* translators: There is a space after the colon. */
+			'execute'              => __( 'Could not execute: ' ),
+			/* translators: There is a space after the colon. */
+			'extension_missing'    => __( 'Extension missing: ' ),
+			/* translators: There is a space after the colon. */
+			'file_access'          => __( 'Could not access file: ' ),
+			/* translators: There is a space after the colon. */
+			'file_open'            => __( 'File Error: Could not open file: ' ),
+			/* translators: There is a space after the colon. */
+			'from_failed'          => __( 'The following From address failed: ' ),
+			'instantiate'          => __( 'Could not instantiate mail function.' ),
+			/* translators: There is a space after the colon. */
+			'invalid_address'      => __( 'Invalid address: ' ),
+			'invalid_header'       => __( 'Invalid header name or value' ),
+			/* translators: There is a space after the colon. */
+			'invalid_hostentry'    => __( 'Invalid hostentry: ' ),
+			/* translators: There is a space after the colon. */
+			'invalid_host'         => __( 'Invalid host: ' ),
+			'mailer_not_supported' => __( ' mailer is not supported.' ),
+			'provide_address'      => __( 'You must provide at least one recipient email address.' ),
+			/* translators: There is a space after the colon. */
+			'recipients_failed'    => __( 'SMTP Error: The following recipients failed: ' ),
+			/* translators: There is a space after the colon. */
+			'signing'              => __( 'Signing Error: ' ),
+			/* translators: There is a space after the colon. */
+			'smtp_code'            => __( 'SMTP code: ' ),
+			/* translators: There is a space after the colon. */
+			'smtp_code_ex'         => __( 'Additional SMTP info: ' ),
+			'smtp_connect_failed'  => __( 'SMTP connect() failed.' ),
+			/* translators: There is a space after the colon. */
+			'smtp_detail'          => __( 'Detail: ' ),
+			/* translators: There is a space after the colon. */
+			'smtp_error'           => __( 'SMTP server error: ' ),
+			/* translators: There is a space after the colon. */
+			'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/data/languages/de_DE.l10n.php

@@ -1,2 +1,2 @@
 <?php
-return ['domain'=>NULL,'plural-forms'=>'nplurals=2; plural=n != 1;','messages'=>['html_lang_attribute'=>'de-DE','text directionltr'=>'ltr','number_format_decimal_point'=>',','number_format_thousands_sep'=>'.','Update %s now'=>'Jetzt %s aktualisieren','[%1$s] Confirm Action: %2$s'=>'[%1$s] Aktion bestätigen: %2$s','[%s] Erasure Request Fulfilled'=>'[%s] Löschauftrag ausgeführt','[%s] Personal Data Export'=>'[%s] Export personenbezogener Daten'],'language'=>'de_DE','x-generator'=>'Poedit 2.2.1'];
+return ['domain'=>NULL,'plural-forms'=>'nplurals=2; plural=n != 1;','messages'=>['html_lang_attribute'=>'de-DE','text directionltr'=>'ltr','number_format_decimal_point'=>',','number_format_thousands_sep'=>'.','Update %s now'=>'Jetzt %s aktualisieren','[%1$s] Confirm Action: %2$s'=>'[%1$s] Aktion bestätigen: %2$s','[%s] Erasure Request Fulfilled'=>'[%s] Löschauftrag ausgeführt','[%s] Personal Data Export'=>'[%s] Export personenbezogener Daten', 'You must provide at least one recipient email address.'=>'Du musst mindestens eine Empfänger-E-Mail-Adresse angeben.'],'language'=>'de_DE','x-generator'=>'Poedit 2.2.1'];

tests/phpunit/data/languages/de_DE.po

@@ -57,3 +57,7 @@ msgstr "[%s] Löschauftrag ausgeführt"
 #: wp-admin/includes/file.php:2415
 msgid "[%s] Personal Data Export"
 msgstr "[%s] Export personenbezogener Daten"
+
+#: wp-includes/class-wp-phpmailer.php:71
+msgid "You must provide at least one recipient email address."
+msgstr "Du musst mindestens eine Empfänger-E-Mail-Adresse angeben."

tests/phpunit/includes/bootstrap.php

@@ -246,10 +246,6 @@
 $multisite = $multisite || ( defined( 'WP_TESTS_MULTISITE' ) && WP_TESTS_MULTISITE );
 $multisite = $multisite || ( defined( 'MULTISITE' ) && MULTISITE );
 
-// Override the PHPMailer.
-require_once __DIR__ . '/mock-mailer.php';
-$phpmailer = new MockPHPMailer( true );
-
 if ( ! defined( 'WP_DEFAULT_THEME' ) ) {
 	define( 'WP_DEFAULT_THEME', 'default' );
 }
@@ -305,6 +301,11 @@ function wp_tests_options( $value ) {
 // Load WordPress.
 require_once ABSPATH . 'wp-settings.php';
 
+// Override the PHPMailer.
+require_once __DIR__ . '/mock-mailer.php';
+
+$phpmailer = new MockPHPMailer( true );
+
 // Delete any default posts & related data.
 _delete_all_posts();
 

tests/phpunit/includes/mock-mailer.php

@@ -1,8 +1,22 @@
 <?php
+/**
+ * Mock PHPMailer class for testing.
+ *
+ * @package WordPress
+ * @subpackage UnitTests
+ * @since 4.5.0
+ */
+
 require_once ABSPATH . 'wp-includes/PHPMailer/PHPMailer.php';
 require_once ABSPATH . 'wp-includes/PHPMailer/Exception.php';
+require_once ABSPATH . 'wp-includes/class-wp-phpmailer.php';
 
-class MockPHPMailer extends PHPMailer\PHPMailer\PHPMailer {
+/**
+ * Test class extending WP_PHPMailer.
+ *
+ * @since 4.5.0
+ */
+class MockPHPMailer extends WP_PHPMailer {
 	public $mock_sent = array();
 
 	public function preSend() {

tests/phpunit/tests/l10n/phpmailerTranslations.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * Unit tests covering PHPMailer translations.
+ *
+ * @package WordPress
+ * @subpackage PHPMailer
+ * @since 6.8.0
+ */
+
+/**
+ * Class Test_PHPMailer_Translations.
+ *
+ * Provides tests for PHPMailer translations.
+ *
+ * @group mail
+ * @group i18n
+ * @group l10n
+ *
+ * @since 6.8.0
+ */
+class Test_PHPMailer_Translations extends WP_UnitTestCase {
+	/**
+	 * Tests that PHPMailer error message translation works as expected.
+	 *
+	 * @ticket 23311
+	 */
+	public function test_missing_recipient_error_message_should_be_translated() {
+		reset_phpmailer_instance();
+
+		$is_switched = switch_to_locale( 'de_DE' );
+
+		$phpmailer = tests_retrieve_phpmailer_instance();
+		$phpmailer->setFrom( '[email protected]' );
+
+		try {
+			$phpmailer->send();
+			$this->fail( 'Expected exception was not thrown' );
+		} catch ( PHPMailer\PHPMailer\Exception $e ) {
+			$error_message = $e->getMessage();
+		} finally {
+			if ( $is_switched ) {
+				restore_previous_locale();
+			}
+		}
+
+		$this->assertSame(
+			'Du musst mindestens eine Empfänger-E-Mail-Adresse angeben.',
+			$error_message,
+			'Error message is not translated as expected'
+		);
+	}
+
+	/**
+	 * Test that PHPMailer error message keys are consistent across implementations.
+	 *
+	 * @ticket 23311
+	 */
+	public function test_all_error_message_keys_should_be_translated() {
+		reset_phpmailer_instance();
+
+		$phpmailer    = new PHPMailer\PHPMailer\PHPMailer();
+		$wp_phpmailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertEqualSets( array_keys( $phpmailer->GetTranslations() ), array_keys( $wp_phpmailer->GetTranslations() ) );
+	}
+}