The question that us see most often, here and elsewhere, concerning the CCA175 is "Do I need to know both Scala and Python?" The answer is yes, there are questions using both languages.
However, please remember that the goal of the exam is to test your Spark knowledge, not your Scala and Python knowledge. The development questions typically provide you some code and ask you to fill in TO-DO sections. So the key is to understand the Spark API. You must have some knowledge of programming, as you will need to be able to read the existing code and understand how to store and retrieve the results you get back from calling the API, but the focus will be on you adding the Spark calls.
There is not a study guide available for this exam, but Cloudera tells us exactly what we will be tested on. For example, the Required Skills at http://www.cloudera.com/content/www/en-us/training/certification/cca-spark.html tell us that we need to be able to join disparate datasets together using Spark. So go look up the join command in Spark. Write a quick five line program in Scala. Then write one in Python. Also, browse the online documentation so you know where to look up the API during the exam (remember you will not have access to a search engine during the exam). Putting in effort before the exam will save you a lot of effort during the exam.