This is not a MediaWiki API client library. For such web API client library with Wikibase access support, see CXuesong/WikiClientLibrary.
This WIP repostiroy contains WikibaseClientLite, an attempt to simulate (a subset of) Wikibase Client Lua API on MediaWiki sites without Wikibase extensions based on a Wikibase items dump. Especially the target MedaiWiki site may retrieve the item information from a LUA-table-based snapshot without direct depenency to Wikibase repository database or Wikibase client extension.
A commandline interface that can generate mw.loadData-compatible Lua data modules containing the Wikibase item information (labels, descriptions, aliases, claims, etc.) from an existing JSON dump of Wikibase entities exported with extensions/Wikibase/repos/maintenance/dumpJson.php. This will later enable retrieving of item information from Lua modules on the target site. This project is still under development.