Undead until the day I die ! ❤✊

Good question! English is a language that relies on context and helper words more than different forms of words, and this can often mean other languages such as Icelandic have many different word forms used differently that all appear to translate to the same thing in English.

"Dansa eða deyja" is the infinitive form: to dance or die, but without the to. It's the neutral dictionary form of a verb. It doesn't make much sense on its own; you probably wouldn't tattoo "to dance" on yourself unless perhaps it was some sort of reference to a longer quote. It's a perfectly correct translation of "dance or die" with zero context, but it's not what the song is called or what the lyric is.

"Dansið eða deyið" is the plural imperative: Matthías is commanding the masses (multiple people) to dance or die. The plural imperative ending -ið is effectively short for "þið", or plural you. Imperatives can function perfectly well on their own as a statement. So that's what the song is called and how the lyrics go. It's probably what you want as the tattoo, if you want to reference the song.

Other possible forms of this phrase that also make sense on their own but with different nuances:

"Dansaðu eða deyðu" is the singular imperative: commanding one person to dance or die. The -ðu (sometimes -du or -tu) ending is derived from "þú", singular you.

Goth girl and Rainbow girl