As per discussion on this thread - https://translatewiki.net/w/i.php?title=Thread:Support/Get_really_%22unreviewed%22_messages_only the un-reviewed messages only show only messages that the current user has not reviewed but translators might want to see messages that have never been reviewed. That URL can be access via this link,
This is how we got the above URL,
When you access the unreviewed translations, you will find in the URL of the page the following string reviewer%3A followed by some number. Delete this number and the %3A that precedes it. Possibly some browsers will show = instead, but it means the same thing.