
Naturally, you can go with whatever interpretation you want. I present my reasons to not think they exist as a thought exercise and not as an imposition of truth. Minifilia's speech is indicative that languages exist, but it is not conclusive. Language is the only barrier she mentions that cannot be empirically proved during the course of the game, pretty much just like historical facts, like the age of Gridania. Except with historical facts you can take them as truth because there are no proofs against those either. And while I can't say there are proofs that languages don't exist (except for the fact they don't seem to affect anything at all), I certainly can say that there are no proofs that they do:
There are barriers of race that can be seen all over Eorzea. Most of the races can be found in certain locations but not in others (Sea Wolves are more numerous in La Noscea, Elezen in Gridania, Highlanders in Ala Mhigo, Miqo'te are everywhere except Ishgard), and there are certain places that have racial problems. The barrier of nations can also be seen in the multiple city-states, with distinct interests that are often at odds with each other. There is also the barrier of creed, most notably between Ishgard and the other cities (and Gridania, if you see the Elementals as having some type of cult in the Padjal), and the fact that each city has a major patron deity that differs from the others. All of these are barriers we can empirically 'prove' that they existed by simply roaming the world, doing its questlines and reading the NPCs.
But then we reach the barrier of language, that is nowhere to be seen. But not only cannot it be seen, which could be handwaved with the Echo, it is never mentioned or referenced outside this one speech that, as I said, is motivational. It doesn't look for accuracy but to boost morale. Minifilia isn't giving the soldiers a history class: she's boosting their morale by showing them how many barriers there are and how little they matter for they are all joined, and one of them -language- might as well not exist.
With all that said, if I had to base any opinion on the "Authors' Intent" (something that I don't subscribe to, but there you go), and supposing the speech isn't the result of lazydom, then it's pretty clear that different languages exist in the world. They just failed at showing the players that they do. They failed at the "Show, don't tell" goal, for whatever reason, which makes things confusing. Specifically, confusing their lack of ability to show with the subject not existing at all.
So I guess we should go ask in the official lore forums and maybe one of the loremasters will tell us what's what.
There are barriers of race that can be seen all over Eorzea. Most of the races can be found in certain locations but not in others (Sea Wolves are more numerous in La Noscea, Elezen in Gridania, Highlanders in Ala Mhigo, Miqo'te are everywhere except Ishgard), and there are certain places that have racial problems. The barrier of nations can also be seen in the multiple city-states, with distinct interests that are often at odds with each other. There is also the barrier of creed, most notably between Ishgard and the other cities (and Gridania, if you see the Elementals as having some type of cult in the Padjal), and the fact that each city has a major patron deity that differs from the others. All of these are barriers we can empirically 'prove' that they existed by simply roaming the world, doing its questlines and reading the NPCs.
But then we reach the barrier of language, that is nowhere to be seen. But not only cannot it be seen, which could be handwaved with the Echo, it is never mentioned or referenced outside this one speech that, as I said, is motivational. It doesn't look for accuracy but to boost morale. Minifilia isn't giving the soldiers a history class: she's boosting their morale by showing them how many barriers there are and how little they matter for they are all joined, and one of them -language- might as well not exist.
With all that said, if I had to base any opinion on the "Authors' Intent" (something that I don't subscribe to, but there you go), and supposing the speech isn't the result of lazydom, then it's pretty clear that different languages exist in the world. They just failed at showing the players that they do. They failed at the "Show, don't tell" goal, for whatever reason, which makes things confusing. Specifically, confusing their lack of ability to show with the subject not existing at all.
So I guess we should go ask in the official lore forums and maybe one of the loremasters will tell us what's what.