There are three options you can set for each site in your ExpressionEngine install. The default language is the language you would like to load by default if the user hasn't specified the language (using the language switcher). You also have the option to include the language abbreviation as a prefix on the url. For instance, if this is set to 'yes' and the user has selected the English language, your urls would be re-written like this: http://mywebsite.com/en/about from http://mywebsite.com/about. The third option is a toggle to enable and disable Transcribe.
Alternatively you can also set the "Add language prefix to URL" to "Defined per Language". When using this option, you will need to set the "Add language prefix to URL" setting on the languages page accordingly