surtranslate
Michael
Surtr

Surtr's speech can be decoded by using a substitution cipher with the following key:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
E N V S I G F J O H L K B M U Y W T D R A C Q Z P X

In-game, the only letters Surtr doesn't use are H and Z. If he does (if he ever will 😔), H will most likely correspond to J, and Z will most likely correspond to X.
Letters with diacritics (ö, ú) are ignored.