Index: src/wp-includes/user.php
===================================================================
--- src/wp-includes/user.php	(revision 44911)
+++ src/wp-includes/user.php	(working copy)
@@ -3143,6 +3143,15 @@
 		return;
 	}
 
+	// Localize message content for user; fallback to site default for visitors.
+	if ( ! empty( $request->user_id ) ) {
+		$locale = get_user_locale( $request->user_id );
+	} else {
+		$locale = get_locale();
+	}
+
+	$switched_locale = switch_to_locale( $locale );
+
 	/**
 	 * Filters the recipient of the data erasure fulfillment notification.
 	 *
@@ -3253,6 +3262,10 @@
 
 	$email_sent = wp_mail( $user_email, $subject, $content );
 
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
 	if ( $email_sent ) {
 		update_post_meta( $request_id, '_wp_user_notified', true );
 	}
Index: tests/phpunit/data/languages/de_DE.mo
===================================================================
Cannot display: file marked as a binary type.
svn:mime-type = application/octet-stream
Index: tests/phpunit/data/languages/de_DE.po
===================================================================
--- tests/phpunit/data/languages/de_DE.po	(revision 44911)
+++ tests/phpunit/data/languages/de_DE.po	(working copy)
@@ -2,13 +2,13 @@
 # This file is distributed under the same license as the 4.9.x package.
 msgid ""
 msgstr ""
-"PO-Revision-Date: 2018-08-13 19:19+0300\n"
+"PO-Revision-Date: 2018-05-15 19:19+0300\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"
 "Plural-Forms: nplurals=2; plural=n != 1;\n"
 "X-Generator: Poedit 2.1.1\n"
-"Project-Id-Version: Development (4.9.x)\n"
+"Project-Id-Version: Development (5.2.x)\n"
 "Language: de_DE\n"
 "POT-Creation-Date: \n"
 "Last-Translator: \n"
@@ -48,3 +48,8 @@
 #: wp-includes/user.php:3445
 msgid "[%1$s] Confirm Action: %2$s"
 msgstr "[%1$s] Aktion bestätigen: %2$s"
+
+#. translators: %s: Site name.
+#: wp-includes/user.php:3175
+msgid "[%s] Erasure Request Fulfilled"
+msgstr "[%s] Löschauftrag ausgeführt"
Index: tests/phpunit/data/languages/es_ES.mo
===================================================================
Cannot display: file marked as a binary type.
svn:mime-type = application/octet-stream
Index: tests/phpunit/data/languages/es_ES.po
===================================================================
--- tests/phpunit/data/languages/es_ES.po	(revision 44911)
+++ tests/phpunit/data/languages/es_ES.po	(working copy)
@@ -2,13 +2,13 @@
 # This file is distributed under the same license as the Development (4.9.x) package.
 msgid ""
 msgstr ""
-"PO-Revision-Date: 2018-08-13 19:19+0300\n"
+"PO-Revision-Date: 2019-03-15 19:19+0300\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"
 "Plural-Forms: nplurals=2; plural=n != 1;\n"
 "X-Generator: Poedit 2.1.1\n"
-"Project-Id-Version: Development (4.9.x)\n"
+"Project-Id-Version: Development (5.2.x)\n"
 "Language: es_ES\n"
 "POT-Creation-Date: \n"
 "Last-Translator: \n"
@@ -44,3 +44,8 @@
 #: wp-includes/user.php:3445
 msgid "[%1$s] Confirm Action: %2$s"
 msgstr "[%1$s] Confirma la acción: %2$s"
+
+#. translators: %s: Site name.
+#: wp-includes/user.php:3175
+msgid "[%s] Erasure Request Fulfilled"
+msgstr "[%s] Solicitud de borrado completada"
Index: tests/phpunit/tests/privacy/wpPrivacySendErasureFulfillmentNotification.php
===================================================================
--- tests/phpunit/tests/privacy/wpPrivacySendErasureFulfillmentNotification.php	(revision 44911)
+++ tests/phpunit/tests/privacy/wpPrivacySendErasureFulfillmentNotification.php	(working copy)
@@ -35,6 +35,24 @@
 	protected static $requester_email;
 
 	/**
+	 * Request user.
+	 *
+	 * @since 5.2.0
+	 *
+	 * @var WP_User $request_user
+	 */
+	protected static $request_user;
+
+	/**
+	 * Test administrator user.
+	 *
+	 * @since 5.2.0
+	 *
+	 * @var WP_User $admin_user
+	 */
+	protected static $admin_user;
+
+	/**
 	 * Create user request fixtures shared by test methods.
 	 *
 	 * @since 5.1.0
@@ -43,7 +61,20 @@
 	 */
 	public static function wpSetUpBeforeClass( $factory ) {
 		self::$requester_email = 'erase-my-data@local.test';
-		self::$request_id      = wp_create_user_request( self::$requester_email, 'erase_personal_data' );
+		self::$request_user    = $factory->user->create_and_get(
+			array(
+				'user_email' => self::$requester_email,
+				'role'       => 'subscriber',
+			)
+		);
+		self::$admin_user      = $factory->user->create_and_get(
+			array(
+				'user_email' => 'admin@local.dev',
+				'role'       => 'administrator',
+			)
+		);
+
+		self::$request_id = wp_create_user_request( self::$requester_email, 'erase_personal_data' );
 		wp_update_post(
 			array(
 				'ID'          => self::$request_id,
@@ -69,6 +100,7 @@
 	 */
 	public function tearDown() {
 		reset_phpmailer_instance();
+		restore_previous_locale();
 		parent::tearDown();
 	}
 
@@ -276,4 +308,121 @@
 		$this->assertFalse( metadata_exists( 'post', self::$request_id, '_wp_user_notified' ) );
 	}
 
+	/**
+	 * The function should respect the user locale settings when the site uses the default locale.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_user_locale() {
+		update_user_meta( self::$request_user->ID, 'locale', 'es_ES' );
+
+		_wp_privacy_send_erasure_fulfillment_notification( self::$request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Solicitud de borrado completada', $mailer->get_sent()->subject );
+	}
+
+	/**
+	 * The function should respect the user locale settings when the site does not use en_US, the administrator
+	 * uses the site's default locale, and the user has a different locale.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_user_locale_when_site_is_not_en_us() {
+		update_option( 'WPLANG', 'es_ES' );
+		switch_to_locale( 'es_ES' );
+
+		update_user_meta( self::$request_user->ID, 'locale', 'de_DE' );
+		wp_set_current_user( self::$admin_user->ID );
+
+		_wp_privacy_send_erasure_fulfillment_notification( self::$request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Löschauftrag ausgeführt', $mailer->get_sent()->subject );
+	}
+
+	/**
+	 * The function should respect the user locale settings when the site is not en_US, the administrator
+	 * has a different selected locale, and the user uses the site's default locale.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_user_locale_when_admin_and_site_have_different_locales() {
+		update_option( 'WPLANG', 'es_ES' );
+		switch_to_locale( 'es_ES' );
+
+		update_user_meta( self::$admin_user->ID, 'locale', 'de_DE' );
+		wp_set_current_user( self::$admin_user->ID );
+
+		_wp_privacy_send_erasure_fulfillment_notification( self::$request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Solicitud de borrado completada', $mailer->get_sent()->subject );
+	}
+
+	/**
+	 * The function should respect the user locale settings when the site is not en_US and both the
+	 * administrator and the user use different locales.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_user_locale_when_both_have_different_locales_than_site() {
+		update_option( 'WPLANG', 'es_ES' );
+		switch_to_locale( 'es_ES' );
+
+		update_user_meta( self::$admin_user->ID, 'locale', 'de_DE' );
+		update_user_meta( self::$request_user->ID, 'locale', 'en_US' );
+
+		wp_set_current_user( self::$admin_user->ID );
+
+		_wp_privacy_send_erasure_fulfillment_notification( self::$request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Erasure Request Fulfilled', $mailer->get_sent()->subject );
+	}
+
+	/**
+	 * The function should respect the site's locale when the request is for an unregistered user and the
+	 * administrator does not use the site's locale.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_site_locale() {
+		update_user_meta( self::$admin_user->ID, 'locale', 'es_ES' );
+		wp_set_current_user( self::$admin_user->ID );
+
+		$request_id = wp_create_user_request( 'erase-user-not-registered@example.com', 'erase_personal_data' );
+
+		_wp_privacy_send_erasure_fulfillment_notification( self::$request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Erasure Request Fulfilled', $mailer->get_sent()->subject );
+	}
+
+	/**
+	 * The function should respect the site's locale when it is not en_US, the request is for an
+	 * unregistered user, and the administrator does not use the site's default locale.
+	 *
+	 * @ticket 44721
+	 * @group l10n
+	 */
+	public function test_should_send_fulfillment_email_in_site_locale_when_not_en_us_and_admin_has_different_locale() {
+		update_option( 'WPLANG', 'es_ES' );
+		switch_to_locale( 'es_ES' );
+
+		update_user_meta( self::$admin_user->ID, 'locale', 'de_DE' );
+		wp_set_current_user( self::$admin_user->ID );
+
+		$request_id = wp_create_user_request( 'export-user-not-registered@example.com', 'erase_personal_data' );
+
+		wp_send_user_request( $request_id );
+		$mailer = tests_retrieve_phpmailer_instance();
+
+		$this->assertContains( 'Confirma la', $mailer->get_sent()->subject );
+	}
 }