Handles registering a new user.

function register_new_user( $user_login, $user_email ) {
	$errors = new WP_Error();

	$sanitized_user_login = sanitize_user( $user_login );
	/**
	 * Filters the email address of a user being registered.
	 *
	 * @since 2.1.0
	 *
	 * @param string $user_email The email address of the new user.
	 */
	$user_email = apply_filters( 'user_registration_email', $user_email );

	// Check the username.
	if ( '' === $sanitized_user_login ) {
		$errors->add( 'empty_username', __( 'Error: Please enter a username.' ) );
	} elseif ( ! validate_username( $user_login ) ) {
		$errors->add( 'invalid_username', __( 'Error: This username is invalid because it uses illegal characters. Please enter a valid username.' ) );
		$sanitized_user_login = '';
	} elseif ( username_exists( $sanitized_user_login ) ) {
		$errors->add( 'username_exists', __( 'Error: This username is already registered. Please choose another one.' ) );

	} else {
		/** This filter is documented in wp-includes/user.php */
		$illegal_user_logins = (array) apply_filters( 'illegal_user_logins', array() );
		if ( in_array( strtolower( $sanitized_user_login ), array_map( 'strtolower', $illegal_user_logins ), true ) ) {
			$errors->add( 'invalid_username', __( 'Error: Sorry, that username is not allowed.' ) );
		}
	}

	// Check the email address.
	if ( '' === $user_email ) {
		$errors->add( 'empty_email', __( 'Error: Please type your email address.' ) );
	} elseif ( ! is_email( $user_email ) ) {
		$errors->add( 'invalid_email', __( 'Error: The email address is not correct.' ) );
		$user_email = '';
	} elseif ( email_exists( $user_email ) ) {
		$errors->add(
			'email_exists',
			sprintf(
				/* translators: %s: Link to the login page. */
				__( 'Error: This email address is already registered. Log in with this address or choose another one.' ),
				wp_login_url()
			)
		);
	}

	/**
	 * Fires when submitting registration form data, before the user is created.
	 *
	 * @since 2.1.0
	 *
	 * @param string   $sanitized_user_login The submitted username after being sanitized.
	 * @param string   $user_email           The submitted email.
	 * @param WP_Error $errors               Contains any errors with submitted username and email,
	 *                                       e.g., an empty field, an invalid username or email,
	 *                                       or an existing username or email.
	 */
	do_action( 'register_post', $sanitized_user_login, $user_email, $errors );

	/**
	 * Filters the errors encountered when a new user is being registered.
	 *
	 * The filtered WP_Error object may, for example, contain errors for an invalid
	 * or existing username or email address. A WP_Error object should always be returned,
	 * but may or may not contain errors.
	 *
	 * If any errors are present in $errors, this will abort the user's registration.
	 *
	 * @since 2.1.0
	 *
	 * @param WP_Error $errors               A WP_Error object containing any errors encountered
	 *                                       during registration.
	 * @param string   $sanitized_user_login User's username after it has been sanitized.
	 * @param string   $user_email           User's email.
	 */
	$errors = apply_filters( 'registration_errors', $errors, $sanitized_user_login, $user_email );

	if ( $errors->has_errors() ) {
		return $errors;
	}

	$user_pass = wp_generate_password( 12, false );
	$user_id   = wp_create_user( $sanitized_user_login, $user_pass, $user_email );
	if ( ! $user_id || is_wp_error( $user_id ) ) {
		$errors->add(
			'registerfail',
			sprintf(
				/* translators: %s: Admin email address. */
				__( 'Error: Could not register you… please contact the site admin!' ),
				get_option( 'admin_email' )
			)
		);
		return $errors;
	}

	update_user_meta( $user_id, 'default_password_nag', true ); // Set up the password change nag.

	if ( ! empty( $_COOKIE['wp_lang'] ) ) {
		$wp_lang = sanitize_text_field( $_COOKIE['wp_lang'] );
		if ( in_array( $wp_lang, get_available_languages(), true ) ) {
			update_user_meta( $user_id, 'locale', $wp_lang ); // Set user locale if defined on registration.
		}
	}

	/**
	 * Fires after a new user registration has been recorded.
	 *
	 * @since 4.4.0
	 *
	 * @param int $user_id ID of the newly registered user.
	 */
	do_action( 'register_new_user', $user_id );

	return $user_id;
}