Common Paorrian Tongue, or simply "Common", is the language spoken by most modern societies in the world.
It originates from continental Paorrian cultures, particularly of the west. It has been adapted over time as the world became more interconnected.
This is a typical convention used in science-fiction and fantasy settings.
It is whatever language that you speak:
If you're Russian and write a story in your native language, they speak what seems just like Russian. If you're an American making an Antiford movie, common sounds like English.