If you trying to Install Magento in your local system using XAMPP. Definitely your Readiness Check will produce error in PHP Extensions Check failed.
1. Go to XAMPP (folder) -> PHP (folder) -> php.ini
2. Search ;extension=php_intl.dll
3. Remove semicolon from above. It would be like extension=php_intl.dll
4. Save and close php.ini
5. Restart Apache from XAMPP