The built in language choice page rests at index.php?a=21. If the url of your site happened to be www.example.com and the Geodesic software was installed in the base directory of that domain the url to the language choice form would be:

http://www.example.com/index.php?a=21

You will see the language choice form allowing the client to choose the language they wish to see the site in. This page will show all current "live" languages within the dropdown as a choice. You can set a language "live" within the languages admin tool. When the client comes to this page their currently chosen language will NOT be automatically selected in the language choice dropdown displayed on that page.

You can also create links that will change the language for you instead of pushing the client through the language choice form. These links can be placed directly in your html design where you need them to be. Find the id of the language you wish to change to within the language admin tool. The language id can be found in a column next to the language name in the languages admin tool. The default language that comes with your installation is "1" and cannot be removed from the site. All other languages added after that obtain their own id. For example if the url to your domain were "www.example.com" and the Geodesic software were installed in the base directory of that domain then to change to a language with the id of 24 you would use a link like that below.

http://www.example.com/index.php?set_language_cookie=24
 
or 
 
index.php?set_language_cookie=24

Of course change the url to your own domain. Also change the "24" to the language id of the language you wish to change to and you should be able to use this as a "language choice" link within your templates (enterprise only) or html to change the language the site is displayed in with one click.