I am looking to learn QA automation using selenium, of the two Java and Ruby which language is more popular?

If you are looking for a straight up comparison you could check out either of the the following to determine which is more popular:

TIOBE -  http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

Or

The RedMonk Programming Language Rankings here - http://redmonk.com/sogrady/2015/07/01/language-rankings-6-15/

In both you can see that Java is the most popular.

Is the question more along the lines of what is more market accepted?

- Or -

Which of the two languages should I use?

Cheers