The Lemeuriel

There's a through-line that connects humanity and it's many disparate cultures. Something that marks us all as kin in the grand scheme of the universe, despite the cultural differences that can make us uncomfortable or incite rage in the less tolerant. The language barrier itself doesn't hinder us from seeing our conversation partner as another person.
Even if one of the god-kings of Baralldaura had crossed paths with a Butcher-Marshal of Uxilgoth, they may hate each other on the principle of who they are, and make claims about the other's lack of humanity, but on a certain level they know they are simply saying such things in an effort to justify that hatred on a deeper level. Lying to themselves at worst. Even the most alienating cultures can be made less so with the proper knowledge and context.
This is not so with the Lemeuriel.
Currently, they hold an... interesting place in history. In fact, they somehow hold two very distinct places.
Once, the Lemeuriel were the might of our world. They built great metropolises, and marvels to rival even that of the Blue Lady by a significant margin. No less than 128 separate nations, both long since crumbled and those still existing, have extensive written accounts detailing those countries' interactions with the Lemeuriel. Hundreds of trade deals negotiated on mediums from clay tablets to early paper, great amounts of what could be considered foreign aid delivered by ships whose descriptions match that of modern multi-masted ships, not to mention the vast war machine that seemed fueled by the infinite power of the Old Gods.
Despite the limitations the Old Gods would have provided, having to essentially beg for a miracle and hope the god in question took pity on you, the Lemeuriel managed to forge a nation that for all intents and purposes would have been a match for any flag currently flying. For all intents and purposes, the Lemeuriel and Lemeuriel alone managed to forge an empire that spanned the world with the help of the Old Gods they followed, and would no doubt have found its way into the forefront of every industry were it still around today.
All of this is simply extrapolated from outside descriptions by contemporaries, as there is no direct evidence of such a nation existing in this world.
There are no ruins, no ancient roads, or long-since abandoned citadels. No trace of lost wealth; buried, looted, or otherwise. No trace of their own written language.
Not even the name of their nation, only being referenced as a people in currently known artifacts and ancient documents.
Just a great big empire-sized hole in the greater knowledge of antiquarian efforts.
The only thing left is the Lemeuriel themselves, gathered in small, out-of-the-way camps.
They're left relatively alone, even by interested academics, because they as a people cause a sense of discomfort and revulsion. I don't mean in the way that people who subscribe to beliefs of racial or national superiority may convince themselves of disgust when faced with their 'enemy', but in the way that many have a fear of spiders or of the ocean. It's uncontrollable, deep-seated, and almost completely universal, a point of specificity that I will cover in more depth later. Despite fairly innocuous cultural rituals that don't even begin to approach the bloodshed of other nations (Ochec and Uxilgoth, for example), and a seemingly complete lack of interest in the political, religious, or ideological goings on in the world, the Lemeriel have been the subject of a completely irrational disdain for the entire time that they have been known to exist.
It carries the sort of consequences of a curse, but one so widespread and powerful that it should be impossible through our current understanding of magic.
As for my previous comment about the disgust that these people cause, and how it is not 'universal', there is a small section of the world's populace that doesn't have the same response as the rest of us. In fact, when exposed to the aspects of Lemeuri culture that should repulse, they find themselves entranced in a way that not even the most fervent and driven academics can match.
If you wish to continue to know this person, I highly advise you never let them be further exposed. Remove them from any sort of direct contact with Lemeuri culture immediately, and keep a close eye upon them for the rest of their natural lifespan so that they do not seek the information on their own and in secret.
Should you let them further their new-found obsession, they will, over time, take great strides in learning the language and customs of the Lemeuriel. Much quicker than those that don't suffer from the same strange difference in outlook, it should be said. One academic I knew described it 'like the man already knew what he was learning, and just had to be reminded.'
Over time, the subject will for the lack of a better term, assimilate into Lemeuri society. They'll learn the language, don their clothes. Eventually, it will be like their mother tongue was not what they've spoken for years. It will only come to them in fits and starts, as the month's pass, not at all. Once that happens, they will likely abandon common society. Simply going out and finding the closest group of the Lemeuriel, and disappear within their number.

Culture

Major language groups and dialects

As far as modern linguists can tell, their language has no dialects in any identifiable form.
Unlike, say, the language you and I speak, where there are branches that have different uses of slang, connotation, and meaning, Lemeuri has only the mother language.
Even though there seems to be no language drift between the many small groups of Lemeuri, the language is nearly impossible to learn. Even those crazy enough to dedicate careers and large portions of their life to it's study and translation can only really hold stuttering conversations of imprecise meaning. The Lemeuri themselves seem to have no interest in actually teaching their language, but there is little to suggest that they actively seek to obscure it.

Common Dress code

It is unknown if their current clothing, which consists almost entirely of cloaks, robes, and hoods, is a traditional clothing choice.
As of now, every Lemuriel enclave dresses identically despite their isolation from one another, not to mention the sheer distance of continents and oceans. Colors remain fairly consistent as well, remaining in fairly inconspicuous blacks, purples, and deep crimsons.

Art & Architecture

It can't really be said that the Lemuriel have a sense of architecture to call their own, given that they simply house themselves in caves and ruins with no effort to resolve the issues that arise from living in such places; like mold or mildew.
Art on the other hand, is perhaps the one cultural identifier they have that doesn't actively drive away those that behold it. Wherever they exist, they paint great murals on the walls depicting strange symbols and unidentifiable images. Given enough time, they will coat every surface of their living space with such paintings, other than the floor. Unlike their language or their rituals, these murals can impart a sense of longing and comfort in the viewer. Uninterrupted, some viewers have been known stare at these paintings for hours without realizing it. In spaces that contain the far more expansive murals, the viewer will even wonder to look at different sections, completely surprised when brought out of their revery that they had moved at all.

Foods & Cuisine

Simple, with little flare.
Their food is not bland, per se, but the flavor is often forgotten completely by those who have tried it. Even those who go out with the express intention of consuming it for knowledge's sake.

Birth & Baptismal Rites

Unknown. These rituals, out of all of those performed by the Lemeuriel, are strangely guarded. Especially in comparison to the normal willingness to share and attempt to explain other cultural practices.
Attempts to view these practices are met with stern response. I have no doubts, that if someone were to attempt to view such rituals by force, such action would be met with a considerable mirrored response.

Common Taboos

The presence of modern gods seems to, for lack of a better term, disquiet the Lemeuriel. It is unknown if this is a positive or negative response, given the message of the Blue Lady, but every Lemeuriel downright refuses to speak or even look directly at gods. They have never offered any sort of explanation for such behavior.

Ideals

Courtship Ideals

There are a few accounts of the Lemuriel marrying into families outside their home country that survive to this day, and they're closely protected as historical artifacts. The most impressive accounts describe, in detail, the actions of courtship taken and the lavish celebrations worthy of any king or queen, even when the subjects in question were closer to the plebs than anything. The detail is great for attempting to figure out how those ancient nations went about their traditions.
Yet, impossibly, none of them are from the Lemuri perspective.