Manual:Hooks/PageContentLanguage

Details

 * $title: the Title object
 * &$pageLang: Language of the page. You should assign a Language object to it, but because other hooks can modify the value, the type can be anything, like a string.
 * $userLang: Language or StubUserLang object; the user interface language

It was added in Title.php but is in content/ContentHandler.php since.

Example
For example, if you want to mark all pages in the namespace with index 200 (and its talk page 201) as being in French, use: