To use Joom!Fish to translate to other languages, you need to have those languages installed on your Joomla! website. Joom!Fish only uses the site languages installed in Joomla!.

You can get your additional languages from http://community.joomla.org/translations. On this page all official translation teams from Joomla! are listed. Just search for the language you need and the go to the link specified.

Then you choose a site language pack and download this to your computer.

In your Joomla! backend via extension > install/uninstall you install your just downloaded languagepack just like you install every other extension.

To show the language on your website, go to Components > Joom!Fish > Languages and tick the active box and save. If you check your the frontend of your website, you should see both flags.