This is possible - when creating a language you don't need to specify the region. 
You can pick a language, Sitecore will fill the region but you may clear it:

[![enter image description here][1]][1]

When doing so, you will end with a language list similar to this:

[![enter image description here][2]][2]

  [1]: https://i.sstatic.net/mmoAE.jpg
  [2]: https://i.sstatic.net/s0Wwy.jpg