How long will it take to learn a Language?

It depends on the circumstances in which you learned that language. For example, if you went to a country to learn its language, it will be easier to grasp it due to the long practicing, which shouldn't take more than three months, whereas if you learned it alone, it would take you longer, around six to eight months.

It depends on situation but if an individual has motivation or interest and also provided same environment of that language then he / she can learn it rapidly.