Atla Criticism - Tumblr Posts

So there are MANY problems with ATLA but one of the things that bothers me a lot is that all of the characters speak the same language. At the beginning of the first season it is made very clear that each of the four nations have no interactions with each other. It is understood that before the war, the air nomads often traveled to other places to experience other cultures. It therefore makes sense that they would speak lots of different languages. However, every single other tribe/nation is extremely isolated and, based on language evolution, there would be no reason for there to be a common language. I understand in theory why it makes a lot of sense for every character to at least be able to communicate through spoken language, but the least they could have done was differentiated the written language between each culture.