https://www.google.com.tr/#q=agar+io+code+language
Detaylı bilgileri alabilirsin sonuçlardaki web sitelerinden.
Bkz ;
Q: Which language has Agar.io been written in?
Answer: Agar.io has been built on C++, HTML 5, CSS and JAVASCRIPT
Q: Which language is used to code Agario Client Side
Answer : Javascript is used as a language to code Agar.io Client side programming
Q: Which language is used to program Agar.io Server Side.
Answer: C++