Another reason for online casinos to list countries could also be for legal reasons. Not all countries are prepared ot offer their own citizens the free will option of online casino gambling. Most countries move in a more liberal and open direction due to the interest of their people and voters. If you wish to be more on the safe side, choose a online casino that supports your country and maybe even language.
Almost all online casinos list countries that they are active in and offer their services. Listing countries can also be a way for online casinos to show how they offer customer support. Even if they dont offer a specific language they could still offer support for that country.