I live in Ikebukuro and I spend most of my day in Shibuya and Shinjuku. I speak enough Japanese to understand people and reply to them. I wouldn't say I'm fluent by any means but I can definitely have a conversation. And navigation? Absolutely not! When I got here I didn't speak at all! The city is laid out so well its extremely hard to get lost and if you do you just find the nearest train station, it'll have maps and even can take you back home. I remember coming here and thought that I would get lost so easily but to be honest its rather hard... I think the only real place you'd get lost is the train stations, especially Shinjuku station I hate that place.