I wish I had done a couple of months of Japanese on Duolingo before traveling there. Simply knowing katakana and hiragana is a huge leap forward from zero knowledge. There were many words I would have known already just from exposure if only I could have read them.
Train line names for example, and all the dozens of english words written in Katakana. You also can't learn from exposure if you can't read the alphabet so I missed out on that too.
I think people should understand that it’s a supplement, and not a solution when you’re on the plane to that country already