Adding
{nwa_translations}
to any page will present a dropdown of the (enabled) languages that will engage the translation.
This would generally go in the Footer HTML of your landing page. But.. you need to remember that Footer HTML is one of the translated texts, so you need to use the translation tool to also put it on every other language otherwise it is only changeable from English.
One workaround for that would be to track down your skin config in Guest>Administration>Plugin Manager: Edit and see if there is a central config area to insert the helper text. This is very skin dependent.