The research may not be very conclusive but it is conclusive on one thing: there is not one single way to learn a language. Of course this comes down to terminology; like what does true success in language learning mean? Does it mean simply being able to be understood, or is it more than that, i.e. being accepted as a native speaker (which is impossible for most people who learn Japanese as a second language by the way, so I say don't focus on being Japanese, focus on being yourself).

That aside, what is known is that there are at least four different things that are definitely needed to learn a second language, and it seems it is your lucky day because I am going to tell you what those four things are! Here is the first:

Comprehensible Input

It's obvious that you need some form of input to learn a language, but if that input is not comprehensible it is not going to be very beneficial for you. In controlled learning situations, the input needs to be at a level where what you don't understand you can guess from context, which generally means understanding of at least 95% of the words being used. Guessing from context is a very useful skill for learning a language as anyone who has acquired a language to a reasonable degree will tell you. Therefore when you teach languages, you should give the students the right opportunities to do this, so when it comes time for them to learn the language by themselves they at least have some strategies for coping with the sometimes very overwhelming input.

Interestingly there is a benefit in not being able to understand the input that you are given, but I think this largely depends on your current level. A study was done on native English speakers before they started learning Russian at university. The students were split into two groups; group A that were not given any extra input, and group B that were shown Russian TV shows and played music. It was found that group B did better on listening and speaking tests, which could be due to the fact that they were able to develop a sound for the language before they actually started using it. In my own experience learning Japanese, I think this sound developed through all the input I got over the years. This also helps explain why it's easier to learn a language if you are in a context where the language is used primarily.