Language popularity on GitHub

The fact that many articles praising Go are written by Python developers doesn't necessarily mean that pythonistas are flocking to Go. It could likely just mean that a few of the people who've hit a performance wall with Python prefer Go to, say, Java.

And you won't necessarily hit a performance wall with Python - it all depends on what you do. Instagram and Pinterest seem to be doing fine using Python.

I think that the rise of Java's presence on GitHub is not so much an increase in Java's popularity, but rather likely a reflection of some companies to be more willing to outsource some parts of their technology stack and commit/post to GitHub.

And also, there are an emerging class of open-source enterprise applications written in Java (Hadoop, HBase and their ilk in Big Data come to mind) which are huge open-source applications and based on Java. Those are likely driving that trend as well.