Best lang to build a chat room

Answer 1

Public chat? Php, html, css, sql and ajax:

Php for your logic; html & css for design; sql for storing data; and ajax for real-time update of ui.

Answer 2

No need to refresh the page with ajax. But yeah, either way works.

Answer 3

Tbh I wouldn't recommend php for that task, since you would have to refresh site every time you send request.
My friend has done chat room by using Node.js with socket.io ^^ you could try it aswell