I went home a few weeks ago and came across a box of old schoolbooks, including my first French and Spanish exercise books. These languages have become a massive part of my life; I lived in and loved Spain last year, while I plan to move to France in the near future. So, it was bizarre to find these books where I spelled bonjour wrong on the first page or clumsily tried out an inverted question mark (¿?) for the first time. It served as an important reminder that a journey of a thousand miles begins with a single step, and that if you take it far enough, your choice of language can have a major impact on your life. You may spend as much, or more, time interacting with a language as you will with some of the people in your life. So how do you make this potentially life-changing decision? My overarching piece of advice would be to give different languages a go, but as you do, consider the following factors:
The sound of the language
Since you are going to be spending so much time with this language, it will help if you like the way that it sounds and if you enjoy speaking it. A good way to get a feel for the sound of the language is by going to a language exchange (most cities have one) and meeting native speakers who can give you a taste of the language, or simply by listening to music, and seeing whether it speaks to you.
Writing system
There is incredible linguistic variety in the world’s languages, and people have different preferences for different writing systems. Perhaps you have always wanted to use and understand characters, like those used in Chinese, Korean, or Japanese? Or if you would like to try out a different alphabet, there are so many to choose from: Greek, Cyrillic, Arabic, just to mention a few. If you feel more comfortable sticking to a Latin alphabet, that gives you plenty of options too, like any of the languages in the Romance and Germanic language groups.
Grammar
There is also immense variety in the grammar of different languages, and if you already have some preferences about different parts of grammar, this might have some bearing on what language you choose. For instance, some languages use more cases while others have none, some have a more rigid syntax, while others do not. Some languages (like Chinese) may even do away with verbal inflection.
Culture