This will vary from person to person depending upon their dedicated time they are providing to master the language. At first , you have to know the basics of the language pretty well so that you will be able to increase your french vocabulary. French is one of the popular language precisely in Europe and it is quite easy to learn. You have to be very careful regarding the grammers of any language. Second , you should have enough knowledge of the second language too - the two languages or more which you are going to use . Generally any language takes a year or more learn completely with full devotions. Language is not just a medium of communication but also conveys one's culture.

Hopes this helps.