How come there is no other language than JavaScript for client side scripting ?

Answer 1

There were. Microsoft had it's vbscript, netscape had javascript. They ditched these and all agreed to pick ECMAScript (javascript) as standard.

For one reason - Convenience. Multiple languages means browsers will need to support multiple tech. That resulted some sites only working in internet explorer and some worked in netscape. You can read more about it in wikipedia.

There is one being developed right now, WebAssembly, by the creator of javascript. Most tech giants like Google, Intel. Apple, Microsoft are backing it up, and it's planned to be replacing Javascript in near future.

Answer 2

there is, php and jquery