Earlier this year there was a bit of social media kerfuffle when, in a piece in The New York Times, the travel writer Pico Iyer was revealed as — despite living in Japan for 25 years — being able to speak only a "smattering" of Japanese. What followed was an considerable amount of indignation that Iyer dared to write about a culture when he couldn't be bothered to learn the language.
I can't comment particularly on Iyer — I've never read any of his books — but the debate got me thinking as to whether you really need fluency in Japanese to write about Japan in an insightful way. I don't think you do. In fact, there are entirely sound psychological, artistic and practical reasons why a critic might deliberately choose not to immerse themselves in the language of the culture they write about.
First, a study in contrast. Unlike Iyer, I spent my 20s immersing myself in the Japanese language. At college I shut myself up in my room learning kanji, much to the detriment of my social life, and when I traveled throughout Japan after enrolling as a graduate student in Japanese literature at a university here, I used to comically refuse to speak to any Japanese people in English. Ever.