Languages

I speak four languages: 2 of them fluently of which I consider one my native language, one fairly and one rudimentarily. I'm trying to make sure that I'm able to speak all four fluently, especially Turkish which I only speak mediocre.
The reason why I especially want to improve my Turkish skills is because I consider myself Turkish, even though I was born in Berlin, Germany and speak German fluently. In addition to that, I consider Germany my homeland.
I just wonder if and to what extend my native language determins my identity.