When loading an item page with an item having an image attached, the WikibaseLocalMedia extension causes the display of a deprecation warning.
Use of Language::factory was deprecated in MediaWiki 1.35. [Called from Wikibase\LocalMedia\Services\InlineImageFormatter::__construct in /var/www/html/extensions/WikibaseLocalMedia/src/Services/InlineImageFormatter.php at line 68]
To reproduce, browse the item revision history back and forth between revisions with and without image. This probably flushes some cache. The deprecation warning is not visible on simple page (re-)loads as soon as the page has been rendered once.