my niche xiv lore obsession is echo translation superpowers and guess what? this is now another place to spill all my headcanons about it!!!!!!
to start off with, this is the canon Encyclopedia Eorzea explanation:
but i refuse to take the "fade and are replaced" part literally. that would mean you're incapable of learning new languages because you physically can't hear them. and that not only raises a ton of practical issues, but also sounds like a curse as much as a gift.
so i prefer to think that instead, when you're talking to someone with the Echo, your brain just tends to gloss over the incongruity between what you're physically hearing and what you're understanding, especially if you're not paying attention. you just assume the other person is speaking your language, because you can understand them. but then maybe you hear a pun, or a song — something that doesn't work in your language — and suddenly you're like "wait, that doesn't rhyme... wait, what did they actually say?"
and maybe it's easier to notice that incongruity the more attuned you are to aether. that would go a long way towards ensuring that every rando NPC you talk to (who would have no reason to know what the Echo is) doesn't freak out about it. i am also working off the assumption that not everyone you meet everywhere you go speaks Eorzean, because why would they?
so really, the Echo would make it easier to learn new languages because you hear a new word and can instantly understand what the other person means by it.
and it is so interesting that it's explicitly about understanding their intentions and not what they actually say. it makes sense, given that ultimately what the Echo does is allow you to "transcend the boundaries of the soul."
but man, there's so much potential there. if someone's having trouble explaining themselves, no worries, you know what they mean. if you're having trouble explaining yourself, they know what you mean! you can listen to someone reciting poetry and understand how they personally interpret the poem... hell, having the Echo means being able to understand Urianger.
i think it would be neat for something like this to become a plot device in canon, even a small one, but it would probably be too confusing to depict. i don't think this is exactly what the writers had in mind anyway; i'm sure they just wanted a way to handwave in-game language barriers. but with the complexity of how language works, it CAN'T be that simple. i really do think that all this is the most logical interpretation of what we're given.
bonus headcanons about ehriyu specifically!!!!!!!
so much of this came about because she's a) Meracydian and didn't speak Eorzean before ARR, and b) a bard.
she relied on the Echo a lot after first coming to Eorzea, but was also hesitant to use it to speak too much, because she didn't know how people would react if they noticed. that's how she got the canon reputation for being silent (insert nod here), even though she's naturally a very loud person.
she loves chatting with people and mildly dislikes reading, because she can't cheat get that extra layer of understanding from the written word. hearing someone tell a story, or recite a poem, gives it so much more life than just seeing ink on a page! that really fueled her love of song that led her to becoming a bard in the first place.
also: she gets literal headaches when people start talking about things she doesn't understand, like advanced academic concepts. because the Echo is trying to make her understand when she doesn't. they're much less acute headaches than the ones that come with visions, but she still has to sit down and have a serious talk with Mikoto about it at one point — like to tell her "you CANNOT keep doing this to me" LMFAO
also also! she is a Miqo'te, and guess what: i ALSO have a lot of thoughts about huntspeak!!!!! canonically, huntspeak involves whistles, and typically in real life, whistled languages are used to communicate long distances!!! and i just think it would be a neat feature to be able to to send whistled messages from malms away that anyone can understand because of the echo. :)
