The direct translation would be "Eso". Therefore your senteces are to be written like this: Eso es bueno. Eso es un perro. Although if I must admit, it's not often used in such way, but rather you'd hear/read them as: Es bueno. Es un perro. Which -even though I ignore the actual reason, and therefore can't faithfully explain it to you- would be some manner of "abbreviation", just as when instead of writing "It is" the "It's" appears: It's good. It's a dog. It is definitely not the same mechanism, but rather just an analogy the one I'm using. Hope it helps!.