Steps to reproduce the issue

Start with fresh install, no sample data.
Create a new article in Uncategorized with some basic content.

Expected result

Should save and go back to editing.

Actual result

The article saves but the system produces a 500 error as it tries to go back to editing. My error log says "PHP Fatal error: Cannot use Joomla\CMS\Language\Multilanguage as Multilanguage because the name is already in use in /Applications/MAMPold/htdocs_joomla4/administrator/components/com_content/Helper/PreviewHelper.php on line 18"

System information (as much as possible)

Joomla 4 alpha 4
PHP 7.0.8
MySQLi database, version 5.0.11
Using MAMP Pro 3.5.2 on Mac OS 10.10.5

Additional comments