Maybe it would be best to get in contact with the Elgg core developers directly via email and/or a message here on the site to make them aware that you want to become a reviewer. There are a few requests open at Transifex (for older version of Elgg even!) that haven't been dealt with for years most likely because they don't get any notifications about these request and therefore just have missed them.

You could try a mail to info@elgg.org or maybe a message to https://elgg.org/profile/jdalsem or https://elgg.org/profile/jeabakker.