"In order to undestand how these systems work I would recommend to know the language in which they are written. The biggest concern with Python is its poor performance hence the knowledge of a more efficient language will be a big plus to your skillset."

What? The Apache stack that's written in Scala recompiles all your code into JVM bytecode, regardless of what language you've written it in. Yes, that includes Scala. Spark isn't actually firing up a python interpreter and running your python code on the data.