In about three years time my friends and I plan on going to Japan for a couple weeks. I'm the one that's going to be the translator because I'm the only one who wants to take the time to learn the language, so I want to get on this right away. I've been self-teaching for a while now, but without much effort, so I know most of the Hiragana, some of the Katakana, a few (10/20) words and a very simple grasp of the grammar.
I understand that the Japanese do not speak English very well (justifiably so, seeing it's not their native language), so how much Japanese should I learn to be able to get by comfortably? If I can master a workbook like, "Japanese For Busy People I", would that be sufficient?