Help me understand the concept of "worlds" and "source"

[Hinoto-no-Ryuji]

To "heal" the universe, they cause a great deal of chaos on the Source and one of the reflected dimensions to weaken the boundaries between them. If that wall comes down, everything on the reflected universe is annihilated and its aether is returned to the Source in a great deluge of chaos and imbalance (a Calamity). They believe that this aether can be funneled to Zodiark to help his resurrection.

Apologies if I'm just misunderstanding the semantics, but this actually runs contrary to my own understanding - I thought that the calamities were deliberately engineered by the Ascians to make Hydaelyn desperate enough to absorb a Shard; ie, the Calamities cause Rejoinings, not the other way around (at least, not on the Source).

[Anonymoose]

Apologies if I'm just misunderstanding the semantics

I'm not sure if a why has been made explicitly clear, but the precise phrasing the game uses across several languages is that The Ardor / The Calamity "blows out the dimensional barrier and causes the dimensions to be merged", and at such a time "every living thing on the reflected world is reduced to aether, and that aether is rejoined to our world".

Different people have understood this in different ways, and I believe you are referencing the theory that a vacuum is created in our world that sucks the shard in, either incidentally (by loss of aether) or by desperation (Hydaelyn choosees to do so to survive). For my own part, I've tried not to interpret it as anything more specific anywhere it isn't needed to build the next tier on a theory's house of cards, lol.

I will grab you an example in just a moment; just need to finish translating something else.
EDIT: WHEW. Done. Apologies for the wait, I'd lost stuff and there was more PVP and excuses excuses excuses.

Word of the Mother / Warrior of Darkness explanations in each language:

Zodiark longeth to be made whole. For His restoration, for His resurrection, His servants labor without cease. They seek to tear down the barriers which surround the Source. Thus do they rejoice in their Ardor─in your calamities─for each marks a Rejoining.

月に追放されたゾディアークは、使徒たるアシエンを使わし、世界を統合しようとしています。
Zodairk, exiled to the moon, is using his Ascian apostles to try to re-integrate the world.

闇の力をより合わせ、完全なる復活を成そうというのです。
By amassing the power of the Darkness, they aim for a complete resurrection.

そのためには、ここ「原初世界」の側から、「世界を分かつ壁」を破壊しなければならない。
To accomplish this, from the side of the "original world" (Source), they must destroy "world-dividing wall".

これこそが「次元圧壊」であり、アシエンたちが「アーダー」と呼ぶ現象なのです。
This is the "Dimensional Crush" (Rejoining), a phenomenon known to the Ascians as "The Ardor".

そして、人の歴史では、これに伴う災厄を「霊災」と呼ぶ。
And, throughout human history, the disaster that accompanies this is called "The Calamity".

Cloîtré sur la lune et bouillonnant de colère, Zordiarche résolut d'accomplir sa vengeance envers Hydaelyn. Il décida d'employer ses fidèles serviteurs, les Asciens, à coaliser les puissances des Ténèbres afin de permettre sa renaissance.
Cloistered within the moon and seething with wrath, Zodiark resolved to accomplish his vengeance upon Hydaelyn. He decided to employ his faithful servants, the Ascians, to unite the power of Darkness and allow for his rebirth.

Pour ce faire, il a principalement besoin d'une chose: détruire la barrière qui sépare le monde primitif des autres.
For this task, he principally requires one thing: to destroy the barrier that separates the original world with others.

Voilà l'Ardor que les Asciens appellent de leurs vœux. Quant aux êtres humains, les nombreuses souffrances qu'ils ont dû endurer les ont poussés à donner un autre nom à ce phénomène: le Fléau...
This is the Ardor for which the Ascians rejoice in welcoming. As for the humans, the numerous sufferings that they had to endure pressed them to don another name upon this phenomenon: The Calamity...

Zodiark versucht, mit Hilfe seiner Jünger, der Ascians, die Dimensionen aufs Neue zu verschmelzen, um wieder zu vollen Kräften zu gelangen.
Zodiark, with the help of his disciples, the Ascians, seeks to fuse the dimensions anew that he might once again attain his full power.

Wenn die Verschmelzung vollbracht ist und alle Welten in ihre Urgestalt einer einzigen Welt zurückgeführt sind, vermag Zodiark mich mit Sicherheit zu überwinden.
When the fusion is complete and all the worlds are in their original unity and returned to a single world, Zodiark will certainly overcome me.

„Nova“ nennen die Ascians die Löschung einer Dimension, das Einreißen der Mauern zwischen unserer Welt und einer anderen. Dramatische Ereignisse, die wir als „Katastrophen“ kennen.
"Nova" (Ardor) is what the Ascians call the extinction of a dimension, the tearing down of the wall between our world and another. Dramatic events that are known as "Calamities".

And so we joined hands with our former enemies, and with their aid came here...to the Source. For there is but one way to restore the balance and save our home: the Ardor. Calamitous destruction with the power to break down the barriers between planes, and see our worlds rejoined.

俺たちの故郷を救う唯一の方法は、この世界でアーダー、つまり「霊災」を起こすこと……そうして次元の壁を壊し、第一世界を原初世界に統合する。
The only way to save our home is to render the Ardor - that is, a Calamity - in this world... This will destroy the dimensional walls and integrete the First to the Original.

Il n'existe qu'une seule manière de sauver notre dimension: nous devons provoquer l'Ardor dans la vôtre. Lorsque ce nouveau “Fléau” sera survenu, il fera sauter la barrière interdimensionnelle et nos deux mondes fusionneront.
There exists only one way to save our dimension: we must provoke the Ardor within yours. When this new Calamity occurs, the interdimensional barrier will be blown out and our worlds will be fused.

Und der einzige Weg zur Rettung ist, eine Katastrophe herbeizuführen, um unsere Welt mit der euren zu vereinigen.
The one path to salvation is a catastrophe that will unite our world with yours.