What languages do you need to know to create web applications?

Answer 1

HTML, CSS, JAVASCRIPT
+
PHP, Ruby or Ruby

Answer 2

Html/Css/JS for user side.
Any language for sever side ( not sure compiled languages, except JAVA semi compiled one, have some web serving frameworks, but it's still possible to do that -- anyway, scripting languages are more efficient to edit/restart without need of compiling time )...

Answer 3

html/CSS for page formatting, js for dynamic pages and PHP for server-side code.

Answer 4

JavaScript only. It can work wonders on both server as well as client side. For HTML and CSS you can use editors and zillions of templates or editors. JavaScript is the King of Web.