Language select: how to set up
Locale module by default provides you a block, Language Switcher, that switches language of the site. It's a list of installed language.

If you like a fancy switcher, you can install this module:
Language Switcher Dropdown


  Language Switcher Dropdown is a very simple module that exposes a new
  block, similar to the default Language Switcher block provided by
  Locale module. The new block allows site visitors to switch languages
  using a drop-down select list instead of using hyperlinks.
  
  The module also integrates well with Language Icons module if
  installed.


Here's an example