Wikidata is a wiki with a structured database (a bit like OmegaWiki), which is used, among other things, as a central repository for maintaining the interwiki links between the various Wikipedias.
In Wikidata, concepts are identified with a unique ID, like "Q41055". This ID gives you the links to the various Wikipedia articles (see: http://www.wikidata.org/wiki/Q208440 ). This is can be compared to the DefinedMeaning at OmegaWiki, which have a unique ID, like "159079" (see: http://www.omegawiki.org/DefinedMeaning:Schachfigur_(159079) ).
DefinedMeaning and Wikidata-ID can be linked one-to-one. Using the Wikidata ID, a link to Wikipedia is automatically retrieved in the user language, and displayed on the side.
Using the Wikidata ID annotation
The "Wikidata ID" annotation is a free-text annotation at the Defined-Meaning level (at the bottom of the page).
To find a Wikidata ID, find the article in the English Wikipedia - or any other Wikipedia that has Wikidata activated. At the bottom of the interwiki links (left column), click on "Edit links". It will take you to the corresponding Wikidata page. The ID is the "Q27868" in the url.
Once you have done that, links to Wikipedia are available for all synonyms and translations of that language, and for all the user languages for which a corresponding Wikipedia article exist.