The current message in MediaWiki core's includes/actions/InfoAction.php and its parameter $1 uses Language::formatDuration:
// Recent number of edits (within past 30 days) $pageInfo['header-edits'] = [ $this->msg( 'pageinfo-recent-edits', $lang->formatDuration( $config->get( 'RCMaxAge' ) ) ), $lang->formatNum( $pageCounts['recent_edits'] ) ];
Its English translation is defined in ./languages/i18n/en.json as "pageinfo-recent-edits": "Recent number of edits (within past $1)",.
On https://translatewiki.net/wiki/MediaWiki:Pageinfo-recent-edits/en people can translate that message to other languages.
"within past $1" is not a nominative case.
This makes the message untranslatable.
It looks like the fix is to split this into separate messages.