What was the first main language in world 400BC?

It's impossible to definitively say what the "first main language" was in the world 400 BC. Here's why:

* No single "main" language: Language development is complex. There were likely numerous languages spoken across the globe at that time, with varying degrees of influence and usage.

* Defining "main": What constitutes a "main" language is subjective. Do we consider the language spoken by the largest population, the language with the most widespread influence, or something else?

* Limited historical records: Our knowledge of languages from 400 BC is limited by surviving written records. Many ancient languages have no written documentation.

However, some languages that were influential around 400 BC include:

* Ancient Greek: A major language of the Mediterranean, used in trade, philosophy, and politics.

* Aramaic: A lingua franca of the Middle East, used in commerce and diplomacy.

* Sanskrit: The sacred language of Hinduism and Buddhism in the Indian subcontinent.

* Old Persian: The language of the Achaemenid Empire, stretching from Egypt to India.

* Latin: A language of the Roman Republic, gaining influence as Rome expanded.

It's important to remember that these are just a few examples, and many other languages existed at the time. The world in 400 BC was a multilingual place, with no single language holding absolute dominance.