Just over 15 million Japanese people speak English, as of 2010. This number represents about 12 percent of the 2015 Japanese population. Many Japanese students go through around 6 years of English education, so they have at least a cursory knowledge of the language.
Many Japanese students who have studied English for several years, only know English words and struggle to make coherent sentences. This is for a variety of reasons, but some people point to the fact that students are rarely able to practice speaking with native speakers and that their instructors tend to focus too much on vocabulary rather than on fluency.