What is the plural of 'Kraken'? [closed]

There are, in general, two ways to form plurals of foreign words in English: to use English rules, or to uses the rules of the original language. This gives us two choices and we have to choose between them.

By English rules, there is no dispute that the plural is Krakens.

To determine the original form, we first have to determine the original language, which commenters on this site, and online references, agree is Norwegian. The commenters that have knowledge of Norwegian have pointed out that Kraken is a definite form. Unfortunately anyone with no knowledge of North Germanic languages will be stuck at this point, so I shall try to explain. Originally, i.e. in Old Norse, there were two equivalent ways of using the definite article. I am not going to give an example in Old Norse for a word that did not exist in Old Norse, but it is as if you could say either en Krake or Kraken, interchangeably, to mean “the Kraken”. (And yes, Krake is the original singular.) As Old Norse developed into Modern Norwegian, the article coalesced with the ending of the word to give what they now call the definite form. Thus we have

although this does vary by dialect. So, since Kraken is not the Norwegian for English Kraken, it is rather difficult to use Norwegian as a model for the English plural!

So how did this error occur? Clearly the main problem is that most English speakers do not speak Norwegian, but we can point to something more specific. It is quite normal to fail to recognise an article in another language. The most common example of this is the large number of words in English that begin with al‑ that come from Arabic, where al is simply Arabic for “the”. No one ever attempts to use Arabic plurals for these words and it is obvious why. Anyone who can say the alcohols clearly does not know what al means, and can thus hardly be expected to know what the correct Arabic plural is.

Thus there is no satisfactory way to use a Norwegian plural, so we had better stick to Krakens. There is certainly no logic behind the use of Kraken as the plural of itself. This may have come about from people trying to use their knowledge of German to work out the plural.

Oxford dictionary defines Kraken and uses the plural of Kraken in an example sentence,

‘Dragons, krakens, giant serpents, griffins, hippogriffs, ogres, evil giants, hydras, and beasts that bore no name at all were among the forces.’

Citation from the book: The Journey to Krakens Cave By Sheridan Injeeli uses the plural form Krakens.

The spell was supposed to grant a wish of any desire, when the Kraken passed away, it's skull was left behind, Legend has it that the skull was located and hidden in the Krakens cave.

Also, there are multiple books using the plural form as Krakens.

On your auxiliary question: herd of Krakens or group of Krakens. I'll say herd of Krakens can be said as- Squad of Krakens on the premises that a giant squid was misunderstood as a kraken- a mythical creature. Description of Kraken is given by Erik Pontoppidan.

From etymonline,

The popular notion of the kraken dates back at least to the time of Pontoppidan (1698-1764), who wrote a description of it. One of the giant squids, as a cephalopod of the genus Architeuthis, might furnish a reasonable basis for the myth.

According to Merriam-Webster's there are two plural forms:

krakens or kraken.

But the graph gives only the first form.

The OP says:

Side question: what is the term of venery (collective term) for Kraken? A school of Kraken? A herd of Kraken? A catastrophe of Kraken?

My answer addresses this part of the OP's question.

Dictionary.com defines kraken as:

a legendary sea monster causing large whirlpools off
the coast of Norway. (emphasis added.)

Thus, the term of venery should be:

A turbulence of krakens.

A whirlpool is an example of turbulent flow. See the picture at Wikipedia, whirlpool. Several whirlpools formed by several kraken close together would be even more turbulent.