I think Ørberg is too extreme. His approach would work better with just a little bit of english thrown in to explain things. Reading his books, I often found myself looking things up anyway.
Hans Ørberg was Danish, so it might have been Danish rather than English if he had decided to include a modern language!
Even though it's often claimed to be appropriate for self-study, I think Ørberg thought that the commonest way it would be used was with a teacher, who would either teach by immersion (I've met people who used it that way) or by speaking a modern language to the students. I'm sure one thing he saw as a benefit to the Latin-only texts is that they could potentially be used by people all over the world, regardless of their native language, without having to be translated or localized for different audiences.
I used Jeanne Neumann’s companion text as a jumping off point into deeper stuff (and because at least a couple of times with just the original text, I spent several pages with the wrong idea for a word and felt embarrassed).
Even though it's often claimed to be appropriate for self-study, I think Ørberg thought that the commonest way it would be used was with a teacher, who would either teach by immersion (I've met people who used it that way) or by speaking a modern language to the students. I'm sure one thing he saw as a benefit to the Latin-only texts is that they could potentially be used by people all over the world, regardless of their native language, without having to be translated or localized for different audiences.