Great example:

When employing her Icelandic code, she pronounces the rhotic "r" - in which the tip of the tongue actually touches the roof of the mouth and makes a sort of almost-trill sound. Imagine her saying the word "start", where the letter "r" involves the tongue touching the roof of the mouth.

In contrast English (aside from a few varieties) is non-rhotic, meaning the "r" phoneme involves the tongue sometimes ALMOST touching the roof of the mouth, but not quite. Think of the word "start" pronounced by a Londoner - sounds more like "staht." Björk is super consistent about using this non-rhotic "r" in English-language contexts.