How do I change my web browser's language?

Welcome to the Apple Support Communities

Normally, a OS X app uses the default language of your system, so the best way to change your browser's language is by changing your Mac OS X language. To do it, open System Preferences > Language and Text, and drag the language you want to use to the top

piccolomini wrote:

How do I change my web browser's language?

Which web browser?

Could you explain what you mean by "language"? The menus? Something about the sites you are going to?