You must consider factors when deciding a language.
1. Work: Can it benefit you in some way?
2. Country: Your country must have a secondary language.
3. Friends: How many of your friends/family speak the same different language?
4. Preference: What language personally appeals to you? (and why?)
5. Significant Other: Does your 'lover' know a second language that has interested you?
6. Language Difficulty: How quick are you to learn a new language, and, how difficult is it to learn compared to other languages around the world?
These are few of the many different factors to find a language that best suits you! You obviously don't need so many factors just the ones I've named to help you decide on a language. Good luck picking the language you desire!