They have mentioned C++ and C# in JD. But they are focusing on data structures, and OS internals. Even through second round was called as design round, they never asked me about OOAD. Even in second round they are more focusing data structure, threads, timing diagram

I don't know how much of these questions still relevant today. Modern languages like C#/C++ already implements linked list , dictionary data structure. Freshers can answer on data structure topic. But that too questions are not straight forward