I am a final year student and am wondering between Java and .NET Core.
Where I live, Java/Spring Boot has a larger market share and is also the majority of what I learn in school. As for C#/.NET Core, it is gradually being chosen by many companies, along with its potential being evaluated by the community recently and through some tutorials I think I quite like it.
Which one should I choose as the first step of my internship?
I would recommend sticking to what you have already spent your time on.
You are in your final year, you spent a great deal of time and effort on Java. The Java has a larger marketplace in your area according to you. So, it would be logical for you to go with it unless you have lost your interest.
I would also like to give the same advice, stick to your current stack. You would start learning other stacks gradully. Don't shift yourself right now.