Extension:Stick to That Language

Stick to That Language allows to choose an interface language in a language selector. The uselang url parameter is used to set that language for the current page and will be added to all links to other internal pages. It introduces a user preferences option to choose preferred languages which will be displayed on top of the language selector.

Download
or with developer access:

Installation
Once you have downloaded the code, place the StickToThatLanguage directory within your MediaWiki 'extensions' directory. Then add the following code to your LocalSettings.php file:

Configuration
This extension comes with some customization options:
 * $egSTTLanguageDisplaySelector : (boolean) Allows to define whether the language selector should be used or not. Default:
 * $egSTTLanguageTopLanguages : (array) preferred languages (displayed on top) for the language switcher for non-logged-in users. Logged-in users can choose their preferred languages, these will be used instead. By default this is set to the busiest languages on Wikipedia. These languages are not used as defaults for the preferred languages user option. Default:  (languages of Wikipedias with the most articles)

To Do

 * Making the user preference option for choosing the languages sortable