Learning Japaneese languge

The best way to learn it is to do a full time course. Before I learned Japanese I studied Mandarin. The drop out rate was almost half. The first year was back home where I learned to read, write, speak, use a Chinese dictionary, translate etc. It was full time, 9 - 4.30 five days a week. The dropout rate was almost 50%. The second year I studied overseas and improved my conversational Chinese as well as learning about culture, history, business Chinese etc. That basis was invaluable for learning Japanese as many of the written characters are the same as Chinese.

The best way to learn Japanese is to do a course, full time if possible so that you get totally immersed in the language. You need to mix with Japanese people so that your conversational Japanese becomes fluent. You ask how many weeks? To become proficient I would say at least one year. But nothing beats living there because that is where your level really improves.