Here's why:
* No official ranking: There's no globally accepted authority that ranks languages based on how many people speak them as a second language.
* Varying definitions: What constitutes a "second language" can be subjective. Some might consider a language learned in school, while others might only consider a language spoken fluently in daily life.
* Regional variations: The prevalence of different languages as second languages varies greatly depending on the region of the world.
However, some languages are often considered contenders for the "second language" title:
* English: English is widely spoken as a second language in many parts of the world due to its historical and cultural influence.
* Hindi: With a large population of speakers in India, Hindi is also spoken as a second language in many parts of South Asia.
* Mandarin Chinese: As the most spoken language in the world, Mandarin Chinese is becoming increasingly important as a second language, especially in Asia.
* Spanish: Spanish is widely spoken in Latin America and is increasingly popular as a second language in the United States and other parts of the world.
Ultimately, the "second language" of the world is a complex concept with no easy answer.