From the FAQ section of their website:
what language does jónsi sing in?
on the first three albums (von, von brigði, ágætis byrjun), jónsi sang most songs in icelandic but two of them (von and olsen olsen) were sung in 'hopelandic'. all of the vocals ( ) are however in hopelandic. hopelandic (vonlenska in icelandic) is the 'invented language' in which jónsi sings before lyrics are written to the vocals. it's of course not an actual language by definition (no vocabulary, grammar, etc.), it's rather a form of gibberish vocals that fits to the music and acts as another instrument. jónsi likens it with what singers sometimes do when they've decided on the melody but haven't written the lyrics yet. many languages were considered to be used on ( ), including english, but they decided on hopelandic. hopelandic (vonlenska) got its name from first song which jónsi sang it on, hope (von).
where can i find sigur rós lyrics and translations?
you won't be able to find lyrics and translations from ( ) because the vocals don't contain lyrics [see question above]. the band had planned to do official translations of ágætis byrjun in 2000 with the help of a grammarian but no progress has been made in this matter. you can read lyrics in icelandic with word-for-word english translations of song titles in our lyrics section.