Sapiens

The group of humans in a currently peaceful human-lead kingdom, call themselves "Sapiens", show for "Homo Sapiens" meaning in their tongue they call "Latin", "wise or knowing man". Their call their kingdom "Regnum Sapientium", "The Kingdom of the Wise", since they have now  known decades of peace, and live peacefully, though warilly, with their neighboring non-humans. Most generally shorten the name to just "Sapientium".

They are surrounded on all sides of the kingdom with non-human lands.

This is pretty much a directly Arthurian setting in this area.

All Elves have a quasi-latin-like approach to language.

The Arthurian Human kingdom was greatly influenced by the High Elves, and thus also takes that on, but as actual Latin.

The humans in this area were originally tribal (Celtic/Gaelic).

All the humans in this area, initially learned the lower “vulgar” tongue of the High Elves during this occupation of hundreds of years. Most of the humans respected but feared this much more advanced people.

Until the High Elves came along and “civilized them”. Later the Elves lost interest, and pull back some of the borders, leaving the humans to fend for themselves. It has been hundreds of years since the Elves left the humans to their own rule in this area. There was war and chaos for centuries, until Uther Pendragon began to unite the kingdoms. Over time, the language of the humans in this area drifted to their own variant of the Elven tongue, that the humans now call “Latin”.

The humans that do not hold on to their old Celtic/Gaelic roots, call themselves the “Latiniatus” after the structure of the Elven tongue.

After the fall of Uther Pendragon, war spread anew, until the rise of Arthur Pendragon.

Arthur has brought peace and prosperity to the human lands of the Latiniatus (as the Elves call them) for many years.

But trouble is brewing, that will directly affect all the surrounding lands and people, human, elf, and otherwise.

Those of Arthur's lands call themselves the Sapiens, from Homo Sapiens “wise or knowing man”.

Their land others simply call "Sapientium".

This only applies to the humans from this “Arthurian Age” part of the world of Beru.