"As a System Administrator, I want to disable the fallback to Wikidata for article descriptions, so that only the local descriptions are used."
We will add a per-wiki configuration option, $wgLocalDescription, which defaults to false.
$wgLocalDescriptionTemplate defaults to Short description. It is the preferred template to use to invoke the short description magic word.
When this is true, requests for the page description in the Action API should return the value of the shortdesc page property, which is set by the {{SHORTDESC:...}} magic word.
Writes to the description should add a {{short description|...} template invocation to the content of the page, or update an existing template invocation.
Descriptions for non-wikitext pages should return an error.