Manual:$wgNamespaceContentModels/ja

詳細
Associative array mapping namespace IDs to the name of the content model pages in that namespace should have by default (use the  constants). 名前空間に対して特殊なコンテンツ タイプを定義していない場合は、その名前空間では  が使用されます (JavaScript ページや CSS ページの特殊な場合を除きます).

JSON
Suppose you have created a new custom namespace   and you want all new pages in this namespace to have JSON content and to be supported by the appropriate content handler. Add the following to your LocalSettings.php file.

$wgNamespaceContentModels[NS_JSON] = CONTENT_MODEL_JSON;

P.S. If you already created pages in this namespace, |see the talk page.