I read in Swedish if a) that is the original language of the book or b) there is no English translation (from a third language) of the book or c) I can't be bothered waiting for the English translation.
I read in Icelandic because a) I think it is the most beautiful language I know and b) because my son sends me the latest book by Arnaldur Indridason every Christmas.
I read - very rarely - in Norwegian because sometimes you just have to struggle with the language if it's the original language of the book. Like Sigrid Undset's 'Förtällingen av Vigdis og Vigaljot' (with Swedish equivalents of the Norwegian letters).
I read - also rarely - in German because I don't want to admit to my wife, a teacher of German and English, that I've forgotten my German.
I do, however, write in English nowadays.