Jiang,

* Wikidata API has not been finalized, and will be rewritten (with some time overlap to allow for migration). See the proposed Wikidata API roadmap, 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=recentchanges and prop=revisions 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 roadmap for other proposed api changes.

-- Yuri Astrakhan (yurik)

P.S. gmail automatically puts your emails into spam because it thinks its a phishing attack (the mail server forwards it as-if it came from you)