This is pretty interesting. I mean I’ve seen dogs dream vividly and am not quite sure how much I believe all them Babe the Pig-alike movies. :)

But I think the definition of a thought is a problem here. Everything we say (or contemplate of saying or trying to remember) is also a thought which precedes our verbal output. Those thoughts will inevitably be in a language of our preference. And actually in process of learning a new language that is often times the pivotal point - once your thoughts switch to a new language, you know you adapted it.