I think it is awesome that you are doing this!

I have had formalized language training and various self-study programs. In general, two months will give you a good foundation for further learning but will rarely give you anything beyond formulated conversations (Where is the bus station? It is two blocks west, etc.). With a structured language program and a lot of work two months can give you a little bit more than this in easier languages (French, for example).

Grammar is the key. A language with easy to grasp grammar (e.g. French) is much easier to excel at and become capable in faster than a more difficult language (e.g. Hindi). French is not easy, but it is MUCH easier than Hindi. I have a friend who took formal Hindi training and said it was the hardest thing he ever had to do.

Once you have basic grammatical concepts down (pronunciation, sentence structure, tenses and cases) immersion is key to build vocabulary. Try to get the grammar before you focus on vocab. I know this is less fun than learning new words but it is so much more important and I cannot stress pronunciation enough. This is also difficult to do because so many of the learn [Insert Language Here] books focus on vocab vs. grammar.

A key companion to immersion is having someone that can explain things to you when you do not understand. Blunt force immersion is not as effective as having someone that can explain difficulties to you in your native language. You need both.

Since you have some Spanish and German knowledge I think French is a great choice. I think Hindi might be a little too daunting. I spent a week in India. I wouldn’t recommend an extended stay there for many reasons (but you do have to see the Taj Mahal before you die), many people speak English, you have to learn a new alphabet, and I think there are more useful languages to learn.

Again, good luck and feel free to PM me if you would like some more info.