apply_filters( 'update_welcome_user_subject', string $subject )

1943	 * Filters the subject of the welcome email after user activation.1944	 *1945	 * @since MU (3.0.0)1946	 *1947	 * @param string $subject Subject of the email.1948	 */1949	$subject = apply_filters( 'update_welcome_user_subject', sprintf( $subject, $current_network->site_name, $user->user_login ) );1950 1951	wp_mail( $user->user_email, wp_specialchars_decode( $subject ), $message, $message_headers );1952 1953	if ( $switched_locale ) {1954		restore_previous_locale();1955	}