That depends on what you mean by “learn”, “the basics” and “new language” (French or Persian will be far easier for you than Japanese). Also, the number of months is irrelevant — the question is, how many study hours will you be able to get in? Anyhow, roughly speaking, you should indeed be able to learn the basics of a new language in three months. You already know English and Hindi, so if the new language is in the Indo-European family, you should be able to reach a nice intermediate level if you are able to put in the hours. Warning: The faster you learn, the faster you’ll forget (unless you do something to review / keep it up). Therefore, an intensive program is only a good idea if you really, really have a use for the language at the end of the three months. If not, well, I’d recommend the slow and steady approach.