There isn't a plural form of it. I can't imagine a situation when it would ever come up.
English grammar note: 'Futhark' is an example of an uncountable noun. Other uncountable nouns include
Futhark is the name of an alphabet. Chess is the name of a game. Neither word has a plural.
Scrabbles anyone?
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "was" is "were."
The plural form of "I" is "we."
elder futhark is the oldest known language of the early rse settlers known as the vikings.
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of the demonstrative pronoun 'that' is those.
Trenches is the plural form.