Go to the Configure Site > Languages/Configs menu tab to manage and add more Languages/Configurations to your website.

This will take you to the list of Languages / Configurations in your website, by default English:

To edit a specific Language/Configuration, click on each of the Edit Configuration icons.  You can also choose the Language/Configuration from the menu on the top of each setup/configuration admin panel page:

Click on the Add Language/Config tab on the top right of the Languages/Configs list page to add a new Language/Config.

You can add an Icon, which can be used in the Languages/Configs Menu you display for your website visitors to choose their Language.  Choose an Abbreviation for the Language/Config to denote that webpages with this suffix is in this Language/Config.  For example, for the default language English, you would leave this blank.  For Spanish, you would choose "spa", for example, denoting that webpages with the suffix "_spa" are in Spanish.  This can be useful when the website visitor switches Languages.  If the page they are on has a compatible webpage, they will be redirected to that page - i.e. page goes to page_spa if available.  Otherwise, they will be redirected to the first position page of that language.

You can choose to populate your new language/config fields from another one, to save time and be easier.  Then you just go in and edit the necessary fields.