For the english translation how about: Next to/Besides a dog is a book man’s best friend.
“Outside” works in english in this case, but “Next to” and “Besides” are even closer in meaning to “neben” while also being more idiomatic English, no?
It’s an old fixed expression in English, and later was used as the setup to a really bad joke: “Outside of a dog, a book is man’s best friend. Inside of a dog, it’s too dark to read”.
In modern English, I’d rather use “besides a dog” or “other than a dog”, but I think “next to” could also work.
It does indeed sound funny if you interpret it literally. I’ve never heard of this expression, and would also use one of the suggested alternatives. I would’ve probably picked “besides”, too.
How about “along with”?
“Along with a dog” sounds a bit clunky to me, but it might work. You could also say “in addition to a dog”, but that sounds a little formal. I think “besides” or “other than” are the most natural choices here.
I dislike the expression “Outside of a dog”. Why use such a weird phrasing, when the English language has so many better alternatives to offer?
Or “Not considering the dog”. Or “Excluding the dog”.
All better than “Outside of a dog”.
Or, simpler, how about simply saying the book is man’s second-best friend, after the dog? Instead of saying the book is man’s best friend, except that it isn’t because the dog is. Instead of knowingly stating falsehoods (“the book is man’s best friend” when it’s only man’s second-best friend) by willingly and intentionally ignoring reality.