Page Language selector for MediaWiki Part 2

So, finally the first version of the Page language selector patch is merged. Yaay 🙂
It is currently deployed for testing on https://dev.translatewiki.net/

There were some changes we made before getting it merged. One of them was to make it an optional feature. Though the Database schema update isn’t really optional, but the code will work only in a case a configuration variable $wgPageLanguageUseDB as true. The variable also controls usage of the SpecialPage and the log for page language.

There are a few shortcomings in the first version:
* There is no way to disallow a user to set the language of the page, me and my mentor are working on a patch which solves the issue using a 'usedb' variable.
* Getting the page language from API doesn’t work.
* A matching API module for setting the page language.
* A protected page’s language shouldn’t be changed by anyone other than an admin.
* Need to better the UI, add error messages.

After succeeding in all this, we need to be able to make it compatible and usable with the translate extension.