Since the rendering of Entity pages depend on the user's language, even for anonymous users, they are currently not cached. This is a big performance issue.
MediaWiki usually forces the parser cache key for anonymous visitors to 'canonical'. This should be overwritten for Wikibase, and a cache key should be generated based on the user preferences, just like for logged in users.
On a related note, we could try to avoid MediaWiki parsing and caching pages directly upon saving them, since it's unclear which cache key is used for that, and it seems pointless for bot edits.
Whiteboard: u=dev c=backend p=0