What language to learn?

I guess the number of native speakers of a language is not a good determinant. Mandarin Chinese, for instance, has almost a billion speakers but you won't have much use of it in the west. It's best to learn a language of a country with rich cultural heritage you can explore (lots of books to read, movies to see) and is fairly influential in the world. If I had to come up with a list of languages I consider most useful for a westerner (but then again, it's just me), it would include German, French, Spanish and Portuguese.

Learn German. A lot of people believe it is a difficult language to learn but it is really interesting and quite simple. It is also quite useful. Germany is Europe's leading industry in technology and the one country that is not in debt yet in the euro zone. Austria is also a beutiful country that you may want to visit before you die. All around it is a great language to learn.....

Spanish or Polish because they are most commonly used.

OR

French or Italian, because they are very beautiful languages. ;)

Learn Spanish. Spanish is spoken in more countries than English is. From a non-biased view, I would say it is useful to learn Spanish as it is English. Buena suerte x

Learn Chinese, Arabic, Hindi, Japanese, French or Spanish. If you do Chinese, Arabic or Hindi or Japanese you might be more in demand because so many people study French, Spanish and German and they are common in the job market.

Spanish is a good language, but no written language has ever bested the masterpiece that is Latin.

Spanish is very much in demand, lots of people to practice it. It's phonetic and the grammar is not too complicated.

Hope this helps

Polish or Japanese.