I personally find that immersing yourself (moving to another country, or joining a groups of native speakers) is probably the quickest way to learn. I speak 2 Germanic languages fluently, and one mostly based in Latin. This allows me to branch out relatively easy into German, Spanish, and pick up some Italian and Portuguese as well, but only for the basics. Spanish would be a good one in the western world, and I would think Chinese is interesting if it wasn't for their writing and 76, or so, dialects. There are about 6000 characters in the Chinese alphabet. Russian could be interesting in that in many former soviet block Countries, it is still commonly spoken as a second language. Either way, you should probably make your choice based on what you think would be the most useful to you. Considering your location; Arabic?