Is it better to learn two languages that are similar or two languages that are very different?

It should not take 4 years to learn any language. Even the most difficult languages for English-speakers can be learned in a year or so. Spanish and French are both similar to English, and if you practice and speak enough, you can probably learn in about 6 months. Also, Spanish and French are similar to each other, so it should not be to hard to finish learning the second one once you finish the first. Spanish and French are both good languages to learn, bot are widely used in the u.s. and around the world. I might suggest Mandarin Chinese, but it is much more difficult. It depends a lot on how much time you spend learning.

learning languages must be done with some selection...... they must be useful, easy to practice, and you are going to use them in regular routiene or some special jobs your selection is fine.... as you know already some Spanish, adding French will be fine. but i fear Spanish is less useful in translation services and in technical fields..... French is fine. Can go for Japanese but needs more than your time limit of 4 years,,,,,,, so you are left only with Spanish and French ....... but learning from books alone may not help...... you have to use the languages..... so in these two you can easily find some one to converse.. ------ by the way i know only english, hindi and telugu-- local Indian languages and have a bit touch with Tamil, Malayalam, kannad ..... south indian languages.... good luck........