That may be off topic, but what is this two-row book layout called in Japanese? And to what extent is this format common?
This layout technique is called 段組み【だんぐみ】, or specifically 2段組み (two-column layout). 段落 (paragraph) is a different concept.
Newspapers and magazines almost always use multiple-column layout. It's not very common in novels, but we sometimes see this layout especially when it's a long, hard-covered one with a lot of short lines.