[Doc] User interface language: How to set "system default"?

Great.

Doesn’t really belong there though, but in the documentation instead. Should be added to http://neos.readthedocs.org/en/2.0/InsideOfNeos/UserInterface/Translation.html

Maybe you would be up for adding it and submitting a pull request? Just click the “Edit on Github”, edit the file and submit for the 2.0 branch (not master). You can find more info on how to do that on Creating a pull request