Q: Do you think writing a journal is a good way to study English?
A: I think it depends on the person. There is no study tool that will be a great fit for every single person. I had a student once, who began to write a journal in English. He would write about what he did each day, then we would go over his sentences to correct his grammar and he would ask about his grammar mistakes until he was sure he understood. He was a very meticulous student, and this practice was really excellent for him and taught him a lot. But most of us are not as meticulous as he is!
I think writing is great practice, because it’s a totally different skill from speaking. BUT, I have noticed that many students feel terrible pressure if they can’t think of a topic, and feeling extra pressure to study often has the opposite effect and causes people to stop. So my answer would be this: If you already enjoy writing a journal in Japanese, then try doing it in English. If you are not a journal writer, try a different writing task like writing a blog entry in English, or pretend you have a penpal and you want to explain Japanese life to that person. Find something that works for you – it doesn’t need to be a journal though!