Based on a limited knowledge of Danish, I'll have a go. Danish, Swedish and Norwegian are similar in written form, although they are very different from one another in pronunciation.
Det Norske Veritas is the name of a corporation, and therefore need not mean anything at all. But it can be interpreted as The Norwegian Truth.
Det is the definite article and Norske means Norwegian. Det Norske means The Norwegian. Veritas, on the other hand, is Latin for truth. The Scandianavian languages have their own words for truth, so veritas must remain Latin, but is a very well-known word as Latin words go .