Darn, they’ve seen through my plans, and now nr 6 won’t allow me to gain citizenship!
It's the classic "are you a terrorist or a member of the Nazi party" question on US entrance forms... the point is obviously not to catch those people, but being able to easily convict them of something (lying to authorities) if they emerge.
The "Japanese language requirement" is technically part of requirement 4... the rational being that if you can't understand Japanese and you aren't wealthy enough to support yourself without working for the rest of your life, you are too dependent on English language workplaces. While they exist, they are a tiny niche of Japanese society in the bigger scheme of things.
Excerpt:
[...] the seven requirements [...] .
Note: Requirement 7 is not explicitly written in the Nationality Law of Japan, which has only 6 requirements. Nevertheless, as a prospective citizen, it is still a good idea to know the language, as it indirectly affects requirement 4 by affecting what kind of jobs you can take.