Jiang,
* Wikidata API has not been finalized, and will be rewritten (with some time overlap to allow for migration). See the proposed Wikidata API roadmaphttps://www.mediawiki.org/wiki/Requests_for_comment/Wikidata_API, and feel free to make suggestions now before implementation begins. Hence - there isn't that much in terms of documentation yet.
* The wikidata extension currently does not extend the action=query, but instead adds its own. Making Wikidata API integrated into the action=query is my prime intention as part of that roadmap. In the future you will be able to do generator=recentchanges&props=wblanglinks to get the list of langlinks from all the recently changed items in one API call.
* At this point all queries like list=recentchangeshttp://www.wikidata.org/w/api.php?action=query&list=recentchanges&rcnamespace=0&rcprop=comment&rclimit=max&rcnamespace=0 and prop=revisionshttp://www.wikidata.org/w/api.php?action=query&titles=Q541001&prop=revisions&rvlimit=max already list all langlink changes to the items, but only by analyzing the comment or the actual change can you check if it was a langlink or a claim change (by using one of the wikibase actions)
* Overall API is moving away from the multi-formats like xml+wddx+php in favor of a single one - json, so in case you are still using xml i suggest migrating. See the main mediawiki API roadmaphttps://www.mediawiki.org/wiki/Requests_for_comment/API_Future for other proposed api changes.
-- Yuri Astrakhan (yurik)
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