Good morning awesome Duolingo team. It would be nice to add a G+ follow button instead of just the Twitter follow and also allow to share our achievements to G+ instead of just Facebook and Twitter. :) Today is a big day for the world, Duolingo for Android is coming out today! \o/
I agree that it is unfair to have Facebook and Twitter but not to have other social networks, but I also wouldn't want to see Duolingo cluttered with many networks icons and links.
Here's the solution I suggest if the team decides to add more social networks: only show those networks that have been linked to Duolingo by the user. I only use Twitter - please show me just Twitter and nothing else. Somebody uses Google+ and Facebook - all right, let them see both.