The thread's summary was edited.
It is not useful to repeat the message content in message documentation.
Is this a header, or is it an sentence with active verb (in other words: it is shown when the indexing is actually happening)?
Those messages starting with "Indexing ..." are all log messages. You are definitely right the documentation needed to be improved. Added to all documentations that they are used in a log file. Thank you for the reports.
Updated the message description: MediaWiki:Bs-extendedsearch-indexing-linked-files/qqq