The Viking Saga

Question

In the Viking lands, we three gods reign supreme

In the three kingdoms, where not all is as it seems.

In the frigid North, En leads the three

Just like in the South, as it should be.

In the temperate South, To makes up the center

The North agrees, but the Middle is the dissenter.

In the Middle, Tre comes in the first

South and North agree, that is certainly the worst.

We gods are amorphous, as it is well known,

Our forms may change in the domains of each zone.

In the extreme lands, En appears like Janus,

Near the Middle, however, they find that heinous.

In the Middle, To appears surprised,

Everywhere else, however, He appears incised.

Only Tre, however, is truly immutable,

Everywhere, His nature is truly indisputable.

What are we? What are the Three Kingdoms?

Hint:

The puzzle hinges on the major local languages of the Scandinavian region, as well as some basic geography to determine their respective regions. While it does require some research, the correct solution will (hopefully) be obvious once it is reached.

The pseudonyms of the Gods don't actually have much bearing on the puzzle, and can be changed without affecting the answers. However, they do act as a (very minor) hint when taken in conjunction with Paragraph 2 of the riddle.

Answer 1

The three gods are:

the three additional letters of the alphabet in...

The three kingdoms, which are (from North to South):

the Scandinavian nations of Norway, Sweden and Denmark.

To be specific:

In Norway and Denmark, En, To and Tre (literally one, two, three) are Æ/æ, Ø/ø and Å/å. In Sweden, they are Å/å, Ä/ä and Ö/ö.

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In the frigid North, En leads the three / Just like in the South, as it should be.

In Norway and Denmark, the first additional letter is Æ.

In the temperate South, To makes up the center / The North agrees, but the Middle is the dissenter.

In Norway and Denmark, the second additional letter is Ø. But not in Sweden, where it is Ä.

In the Middle, Tre comes in the first / South and North agree, that is certainly the worst.

The third additional letter (in Norway and Denmark), is Å, which comes first in Sweden.

In the extreme lands, En appears like Janus, / Near the Middle, however, they find that heinous.

Æ is like Janus in the sense that it has two faces, A and E.

In the Middle, To appears surprised, / Everywhere else, however, He appears incised.

The Swedish Ö looks like a surprised face, whereas the Norwegian/Danish Ø, is visually cut in two (incised).

Only Tre, however, is truly immutable, / Everywhere, His nature is truly indisputable.

Only Å is shared between all nations.