There are certain bars and such where you can get Japanese girls easily even if you don't speak Japanese at all. Those are the places where the "gaijin hunters" go to find a cool foreigners to have sex and learn English with. BUT. In my opinion, the level of those girls isn't that high. And they always seem a little crazy or something. I don't know. By learning Japanese you can start a conversation with anyone. If you're good looking you can easily give it a go with those Tokyo Drift kinda girls and even if you're just a normal guy you can find pretty awesome girls because there's a lot of Japanese girls who are genuinely interested in foreigners but they don't have what it takes to communicate in English...