Universal Language Selector/Analytics

The Universal Language Selector (ULS) has been deployed on Wikimedia wikis since July 2013. This extension allows the users to select their user interface language, as well as define their settings for webfonts and input methods. As a component, ULS is also used for selecting a language in other contexts, for example—the target language for translation.

Given that it's a very feature-rich extension, the developers are interested to know how its different parts are used, so that they can be improved.