Wikipedia has a nice API that can return values in a variety of formats. You'll have to process the wikitext yourself, though.

E.g. to return the text of the article about 27th of December, wrapped in a JSON structure: https://en.wikipedia.org/w/api.php?action=query&prop=revisions&format=json&rvprop=content&rvlimit=1&titles=December%2027

You can view the API reference at https://en.wikipedia.org/w/api.php , read more at https://www.mediawiki.org/wiki/API , and play with it in your browser at https://en.wikipedia.org/wiki/Special:ApiSandbox .

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Matma Rex