GlotPress custom route for Register page, gp-includes/routes/register.php.

register.php

<?php
/**
 * Registration Class
 *
 * Allow users to create new accounts
 */
class GP_Route_Register extends GP_Route_Main {
  // GET variables
	function register_get() {
		// If user is already logged in
		if ( GP::$user->logged_in() ) {
			// Send him to homepage
			$this->redirect( gp_url( '/' ) );
			return;
		}
		// Load template
		gp_tmpl_load( 'register', array() );
	}

	// POST variables
	function register_post() {
		global $wp_users_object, $wp_auth_object;

		require_once( GP_PLUGINS_PATH . '/recaptcha/recaptchalib.php');
    // Replace $privatekey with your own 
    // Get it from https://www.google.com/recaptcha/admin/
		$privatekey = "your private key";
		$resp = recaptcha_check_answer ($privatekey,
			$_SERVER["REMOTE_ADDR"],
			$_POST["recaptcha_challenge_field"],
			$_POST["recaptcha_response_field"]);

		if ( !$resp->is_valid ) {
			// What happens when the CAPTCHA was entered incorrectly
			$this->errors[] = __("Yay! are you a bot? Please enter the CAPTCHA code");
			$this->redirect( gp_url_register() );
			return;
		}

		// Check for full name
		if( empty( $_POST['user_nicename'] ) ) {
			$this->errors[] = __("Please tell us your full name");
			$this->redirect(  gp_url_register() );
			return;
		} else {
			$_POST['user_nicename'] = htmlspecialchars( $_POST['user_nicename'] );
		}

		// Check for username
		if( empty( $_POST['user_login'] ) ) {
			$this->errors[] = __("Please choose a username");
			$this->redirect(  gp_url_register() );
			return;
		}

		// Check for email
		if( empty( $_POST['user_email'] ) ) {
			$this->errors[] = __("We need your email address");
			$this->redirect(  gp_url_register() );
			return;
		}

		// Check for password
		if( empty( $_POST['user_pass'] ) ) {
			$this->errors[] = __("Please set a password for your account");
			$this->redirect(  gp_url_register() );
			return;
		}

		// Get username by login
		$user = GP::$user->by_login( strtolower( htmlspecialchars( $_POST['user_login'] ) ) );
		// Get user by email
		$user_email = GP::$user->by_email( strtolower( htmlspecialchars( $_POST['user_email'] ) ) );

		// If username exists
		if ( $user || is_wp_error($user) ) {
			// Ask for a new one
			$this->errors[] = __("Sorry that username is already taken, please pick a new one.");
			$this->redirect(  gp_url_register() );
			return;
		}

		// If email exists
		if( $user_email || is_wp_error($email) ) {
			// Ask for a new one
			$this->errors[] = __("That email is already registered, please log in.");
			$this->redirect( gp_url_login() );
			return;
		}

		$args = array();
		$args['user_login'] = htmlspecialchars( $_POST['user_login'] );
		$args['user_pass'] = htmlspecialchars( $_POST['user_pass'] );
		$args['user_nicename'] = htmlspecialchars( $_POST['user_nicename'] ) ;
		$args['display_name'] = htmlspecialchars( $_POST['user_nicename'] ) ;
		$args['user_email'] =  htmlspecialchars( $_POST['user_email'] );

		$new_user = GP::$user->create( $args );
		if ( !$new_user ) {
			$this->errors[] = __("Sorry that didn't work, please try again");
			$this->redirect( gp_url_register() );
			return;
		} else {
			$this->errors[] = __("Your account has been created, please log in.");
			$this->redirect(  gp_url_login() );
		}
	}
}
?>