Learning a new language has been always difficult for us adults, when compared to a kids, growing up they can easily grasp language easily.
Now this post is all about learning a new language which you have no knowledge. We will be focusing on Japanese.
Yes, in 40 days you will be able to understand and read Japanese and all you have to do is give 15-30 mins daily and you will be fine learning the new language.
There is a website duolingo.com (here you will learn many languages). Sign up and start with Japanese. There are 40 Levels, complete each level daily. As you will reach the level 40, you will have a good understanding on Japanese.
Many people might not be able to complete every level in one day, but if you really want to learn this language and you can push yourself, then there will no problem. Just give 15 mins in morning and 15 mins in the night. (I mean seriously hardcore concentration of 15 mins).
Following this process will make you learn the Japanese fastest. Just keep practicing more everyday, and practice completed levels to revise.
This is process that will make learn any new language in couple of weeks. (4-6 weeks)
Advice : Keep the duolingo app with you, revise in washroom, when sitting alone, or waiting for someone. (15 mins of day and night are most important, before sleeping and after waking up).