I don't use the language selector myself because I just use the en-AU option. But I did a blank install using the catalook template which required me to install all the options and I think from what I saw it allows different currencies to be set on the site, with different tax levels - mainly used in areas that have multiple tax rates.
I'm not 100% sure, but I think there could be an option as well within the product listing to put in different languages in the products for sale, so the different languages installed could utilised.
This is a German based product so in Europe they are big on localisation whereas for me, in AU it's not such a big issue.
You could still use DNN search but the language switcher does more in reference to the pricing and product language options from what I understand with my limited use.