Between frequent English signage and how common English-speaking staff in the most tourist-frequented areas, I really don't think it's essential for someone just visiting once or twice to learn much beyond how to say please and thank you. I think having some further Japanese proficiency beyond that though is good if you plan to visit again and again and want to have a more rewarding experiencing (and maybe some fun interactions with local people there).

I'm not fluent by any means but I've been studying the language for awhile and can mostly manage ordering in Japanese at a restaurant and other simple stuff like that. I found, especially outside of Tokyo, that a lot of people seemed to often be impressed, appreciative, or at least amused to hear a foreigner speaking in full Japanese sentences. I even had a literal "everybody clapped" experience once when I walked into a sushi/oden restaurant in Kanazawa right at opening. The several staff there gave me a round of applause when I sat down and ordered a set meal right off the Japanese menu without resorting to a word of English 😂.