I don't think it's okay to simply assume that a race has a native tongue that it knows of just because you believe it "makes more sense". This is a fantasy setting after all, with a very different history and timeline than the one that resulted in the conventions of the real world. It is hard to say whether such conventions can possibly be applicable.
If the lore doesn't say that they do, go with that. Don't go with "it doesn't say that they don't"--it doesn't say that the Hyur don't have their own language, or even that the Hyur don't have five languages. It's safer to simply not presume.
I'll show you why. Of all the races, only the Roegadyn and the Miqo'te have been mentioned in the lore to have a racial language.
Of the Roegadyn:
"...[M]any Roegadyn words have been forgotten after generations of disuse, with only popular terms being passed down through names. Every so often, however, a new (or should I say old) word is rediscovered in an ancient tome and added to the list for further generations to use (or ignore)."
http://forum.square-enix.com/ffxiv/threa...onventions
So their language is dead. The Roegadyn don't speak it at all, because much of it is lost to them.
Of the Miqo'te:
"The names of these tribes contained many sounds which were difficult to represent with the existing Eorzean alphabet; but the fact that there were the same exact number of tribes as letters in the Eorzean alphabet was taken as a sign that they were destined to make the new realm their home, and so assigned each tribe with a letter/sound that was closest to its name. Over time, this resulted in the changing of the pronunciation to more closely resemble the pronunciation of the Eorzean letter than that of the original word."
The Miqo'te came to Eorzea during the Fifth Umbral Era, at least fifteen hundred years prior to the present time. And when they came over, they began adopting the way of speaking that the locals used. If they had a language, it could very well be dead to them by now, as the original pronunciations of many of their words have been lost to time.
Of the Elezen, SE tells us that their names have French pronunciations, but they also tell us that the Elezen don't know why that is the case:
"One will also notice that some of the Elezen names appear familiar to those of the Hyur.
"Louis vs Louisoix
Eugene vs Eugenaire
Arthur vs Arthurioux
"Gwen vs Gwenolie
Hilda vs Hildie
"There are Eorzean historians who believe that these similarities in names may be proof that the two races are of similar origin─’open-minded’ Hyuran historians claiming the Elezen are a bastard race spun off from the Hyurs (and not the other way around). Elezen historians, on the other hand, simply deny any blood relation whatsoever."
Their naming conventions are ancient, but neither the Hyur nor the Elezen are mentioned as having conventions in some racial language that explain these conventions.
The Elezen have been on Eorzea for thousands of years, whereas the Hyur came onto the continent a thousand years ago. So it isn't even clear who was using the "common tongue" first. But it's stereotypical to consider the "common" or "default" language to be that of FFXIV's "human" race.
TLDR, the lore contradicts the idea of the five main races having unique spoken tongues among them, and the idea that the common tongue is the Hyuran tongue isn't even something that can be confirmed.
So it might be rather dodgy to roleplay that you can speak "Ancient Roegadyn," or to speak French in-game as an "Elezen language."
As for the Echo and how it allows people to understand the languages of other races, well... isn't that handy for understanding beastmen, dragons, and ancient runes, rather than common races that do regular business in every city-state?
If the lore doesn't say that they do, go with that. Don't go with "it doesn't say that they don't"--it doesn't say that the Hyur don't have their own language, or even that the Hyur don't have five languages. It's safer to simply not presume.
I'll show you why. Of all the races, only the Roegadyn and the Miqo'te have been mentioned in the lore to have a racial language.
Of the Roegadyn:
"...[M]any Roegadyn words have been forgotten after generations of disuse, with only popular terms being passed down through names. Every so often, however, a new (or should I say old) word is rediscovered in an ancient tome and added to the list for further generations to use (or ignore)."
http://forum.square-enix.com/ffxiv/threa...onventions
So their language is dead. The Roegadyn don't speak it at all, because much of it is lost to them.
Of the Miqo'te:
"The names of these tribes contained many sounds which were difficult to represent with the existing Eorzean alphabet; but the fact that there were the same exact number of tribes as letters in the Eorzean alphabet was taken as a sign that they were destined to make the new realm their home, and so assigned each tribe with a letter/sound that was closest to its name. Over time, this resulted in the changing of the pronunciation to more closely resemble the pronunciation of the Eorzean letter than that of the original word."
The Miqo'te came to Eorzea during the Fifth Umbral Era, at least fifteen hundred years prior to the present time. And when they came over, they began adopting the way of speaking that the locals used. If they had a language, it could very well be dead to them by now, as the original pronunciations of many of their words have been lost to time.
Of the Elezen, SE tells us that their names have French pronunciations, but they also tell us that the Elezen don't know why that is the case:
"One will also notice that some of the Elezen names appear familiar to those of the Hyur.
"Louis vs Louisoix
Eugene vs Eugenaire
Arthur vs Arthurioux
"Gwen vs Gwenolie
Hilda vs Hildie
"There are Eorzean historians who believe that these similarities in names may be proof that the two races are of similar origin─’open-minded’ Hyuran historians claiming the Elezen are a bastard race spun off from the Hyurs (and not the other way around). Elezen historians, on the other hand, simply deny any blood relation whatsoever."
Their naming conventions are ancient, but neither the Hyur nor the Elezen are mentioned as having conventions in some racial language that explain these conventions.
The Elezen have been on Eorzea for thousands of years, whereas the Hyur came onto the continent a thousand years ago. So it isn't even clear who was using the "common tongue" first. But it's stereotypical to consider the "common" or "default" language to be that of FFXIV's "human" race.
TLDR, the lore contradicts the idea of the five main races having unique spoken tongues among them, and the idea that the common tongue is the Hyuran tongue isn't even something that can be confirmed.
So it might be rather dodgy to roleplay that you can speak "Ancient Roegadyn," or to speak French in-game as an "Elezen language."
As for the Echo and how it allows people to understand the languages of other races, well... isn't that handy for understanding beastmen, dragons, and ancient runes, rather than common races that do regular business in every city-state?
My larger point was that the Echo means that any linguistic issues are immaterial for PC adventurers (at least those who RP having the Echo, and RPing that you don't actually presents a whole other set of major issues). Basically, I argue that you can assume a common tongue exists, that (very nearly) every being speaks it, and for anyone who doesn't, the Echo makes it irrelevant in RP.