The plural version of this message creates a grammatically incorrect sentence: "The latest version of these pages have been marked for translation". Since 'version' is always singular, that should be "The latest version of these pages has been marked for translation".
Consequently, the source version of this message should read:
The latest version of {{PLURAL:$1|this page|these pages}} has been marked for translation.
URL: https://translatewiki.net/wiki/MediaWiki:Tpt-old-pages/ia