To support two core issues for Drupal 8, namely #568986: Dynamically update standard language list from localization server and #1337628: Enhance language select form with textbox and other tools, we need to include some more information in the language list XML (and possibly rename it to something more generic). The current language list is hosted at http://localize.drupal.org/l10n_server.xml. It does have English and native names of languages and language code. That is it.

1. We need the direction of the language added (LTR/RTL) for completeness.
2. For #1337628: Enhance language select form with textbox and other tools, we'd need indication in the XML of the completeness of the languages. I think this is best approximated by the Drupal core (featured project) progress percentage communicated in the XMl. That issue might end up actually displaying the value to the user or hiding some languages based on that data.
3. To make this more generic, I think we should rename the file to languages.xml or somesuch.