What is the "prayer" being said when Elsa was being crowned?

Evidently the language is Norse, possibly an older dialect (the source I have on that doesn't seem very reliable to me).

As noted in the comments bellow, when plugged into Google Translate, the detected language is Icelandic.

Unless someone familiar with either language can confirm for sure, this is about the best I can find at the moment.

The line from the movie:

"Sem hon heldr inum helgum eignum ok krýnd í þessum helga stað ek té fram fyrir yðr...Queen Else of Arendelle."

In English:

"As she holds the holy properties, and is crowned in this holy place, I present to you... Queen Elsa of Arendelle."

Source for the translation.

It's old west norse, from which the modern Icelandic language descends. That's why Google Translate identify it as Icelandic.

Read more about the Old Norse dialects and descendants at Wikipedia.

To pepper the script with authentic Norwegian words, accents and phrases, filmmakers called on Jackson Crawford, who teaches Old Norse, Scandinavian mythology, Vikings and sagas at UCLA. His research focuses on the history of Old Norse. “Sem hon heldr inum helgum eignum ok krýnd í þessum helga stað ek té fram fyrir yðr…” Translated: “As she holds the holy properties, and is crowned in this holy place, I present to you…” "QUEEN ELSA OF ARENDELLE!!"

I am pretty sure that this is Old Norse. I'm Icelandic and I can read this text, but this isn't Icelandic. The form is very similar to the old Icelandic Sagas.

It must be Icelandic Because the owner of the training post that Anna meets on her way to find Elsa says " I add a quart of lutefisk for forgood feelings"...lutefisk is a common Nordic dish. There are actually a lot of Nordic references in the movie...kind of interesting.