(Shrug) I live in the northeastern United States.

To state the obvious, Mexico is to the south of us and Quebec is to the north of us, so it is no surprise that Spanish and French are high on our list of popular languages.

Less obvious, but probably more important, we have a cultural attachment to England. When I was a kid it was much more common to travel to Europe than to any other continent--some of it a distant inheritance from the days when educated Europeans took the Grand Tour--and we are attracted to the languages of the countries that neighbor England. 

Quickly checking, our local high school offers courses in French, Italian, Latin, and Spanish. Three European languages, and one holdover from the days when Latin was an entrance requirement to the elite colleges... why? ... because it was required at Oxford and Cambridge... why? ... because it was the language of the Western branch of the (Catholic) Church in the middle ages.

Your facts are messed up. Hindi is 4th with 490 million; German has 166 million; Norway has about the 25th highest GDP, or 5th highest GNP, although I think GDP is more attractive than GNP to immigrants, etc.

I think one factor might be the extent to which some of these languages are taught. French and Spanish are widely taught in Europe and North America. I wouldn't like to speculate but I would hazard a guess that Vietnamese and Bengali aren't widely taught around the World except inside the countries that speak those languages. There are lots of French and Spanish immigrants across the World, this is true of Germans also.

To speak of my own experience, I'm learning Spanish to a high degree because I live here in Mexico. There's a high number of speakers all over the World, not just in Spain, which means it's useful for travel across the World, a big plus for someone who wants to travel, especially in the Americas. Also, it's a relatively easy second language for me to learn as it's similar in many ways to my mother tongue. When successfully acquired to my satisfaction, Spanish will be a great motivator for studying other languages!

There's only 80 native German speakers? haha. I'm just kidding. 

I think there is no reason that so many people gravitate towards certain languages. Rather, I think there are hundreds of reasons. Over the years, I've been attracted to learn so many languages. From a young age, I was obsessed with Japanese culture and history. I tried to learn from a book at college. I memorized all the hiragana and katakana (which I've long forgotten) but never got much further. It wasn't my time to learn a language, nor was Japanese accessible to me at that time. Next was Swedish. I fell in love. Learned it to a point further than I learned Irish way back at school and definitely a lot better than Japanese. With a Swedish girlfriend, the language was accessible. I had just left college so I had free time. It was the right time maybe. We broke up and as you might imagine, I stopped studying. Next was Chinese. I met some really cool Chinese guys and they taught me basic words. Then I got serious. I had just found a job and I was throwing my newfound wealth at my Chinese language learning pursuit. Funnily enough it worked quite well as a catalyst. My Chinese pronunciation was decent. My knowledge of characters growing. I decided to go to Belgium for a weekend break, brussels more specifically. I thought a break from Chinese was in order. I started brushing up on basic high school French. It was really bad. Not worth the break from Chinese. Now, only a few months later, I've fallen in love with a Polish girl. 

Why do people learn certain languages? Because people are insane. Don't look for logic. We're all crazy!

i think this not related to how rich is this country , Indian language is the world second most spoken language because of number of indian people themselves , only their huge number make it the second language , but not bacause it is spoken by many peolpe all over the world "not only by its people ". on the other hand English can be used by all people all over the world.