What are the four most commonly spoken first languages?

The four most commonly spoken first languages in the world are:

1. Mandarin Chinese: Spoken by over 1 billion people.

2. Hindi: Spoken by over 600 million people.

3. English: Spoken by over 370 million people.

4. Spanish: Spoken by over 530 million people.

It's important to note that these numbers can fluctuate and depend on how "speaker" is defined (e.g., native speaker vs. second language learner).