Hello, there are a few causes for 500 Internal Server Errors, I'll detail the 2 most common below:
1. Make sure that Directories/Folders have their permissions set to 755 and PHP files have their permissions set to 644. Having 777 or 666 permissions causes 500 Internal Server Errors for security reasons (as the 6 or 7 in the last digit indicates "writable by everyone"). You can check permissions in either the cPanel File Manager or via FTP. Since I see you're installing MediaWiki, make sure that the images directory is 755. I know that the installation guide says 777, but this is not necessary on x10Hosting due to how PHP is set up.
2. Delete or post the contents of any .htaccess files you have. You may need to select the "Show hidden files and folders" option in cPanel File Manger or in FTP before being able to see these files. An improperly-formatted .htaccess file is a common cause for 500 Internal Server Errors.
