Applying for MS in CS - what are the programming languages I must know before starting graduate school? I am an electrical engineer with basic programming skills in C, C++, Python and Java. I wish to pursue my masters in computer science to pursue research (PhD) after working for a couple of years in the IT industry (preferably product development). 

So what are the programming languages one must master before starting graduate school - MS in CS?
You don´t need any specific languages.

Try to get your "basic" skills in (some of) the languages you already know to an "advanced" or "expert" level. Doing this you will automatically understand and internalize the concepts behind the programming languages.

All the rest is just syntax and you will be able to pretty much learn many other languages "on the fly" if needed.