Is it necessary to focus on one particular language?

I am a student having had a few intern jobs. All of them use a different technology stack: Python, Java,C/C++, C#, R, ObjC/Swift. Although I personally feel I am most familiar with Java among these language.

My question is, is there any benefit to continue enhance my Java skill? or should I evenly allocate my time to all the technologies?

eg. occasionally, I participate in some coding challenges which focus on abstract algorithm and is fairly language-independent. In this kind of cases, should I use the opportunity to practice the language I am more familiar with, or the languages where my memory & knowledge is fading?