Unable to create Joomla user account through CiviCRM profile
This issue is coming in case of multilingual site.

To resolve this issue , go to Root/components/com_users/models/registration.php,near line no. 307 find below mentioned code

    if (JLanguageMultilang::isEnabled())
    {
        $form-&gt;setFieldAttribute('language', 'type', 'frontend_language', 'params');
    }

    if (empty($form))
    {
        return false;
    }


Replace with

if (empty($form))
{
    return false;
}

if (JLanguageMultilang::isEnabled())
{
     $form->setFieldAttribute('language', 'type', 'frontend_language', 'params');
}


Try this solution.