Back in the day, Nihongo Journal (along with the venerable Mangajin--requiescat in pace) was the magazine many Japanese learners were eager to snatch up at the newspaper stand before the one or two copies they stocked were gone.
Sadly, both passed on. Mangajin around 1998 and Nihongo Journal in 2005.
I asked my magazine supplier to send us the nearest equivalent: "Give me a magazine all about Japanese," I asked. Blinded by sadness, I accepted this one (Monthly Nihongo) without doing any research. Well, the magazine is indeed all about Japanese, but instead of learning Japanese, it is about teaching Japanese.
It is still very interesting--especially if you are in to linguistics. But the language is native-level Japanese and is not appropriate for anyone less than an advanced student. If you are such a student and you like learning about learning Japanese, this is definitely for you.