Historically, the dominant language in southern Mesopotamia was Akkadian. This Semitic language was spoken from around the 3rd millennium BCE until the 1st century CE. It was the language of administration, literature, and daily life.
However, after the decline of the Akkadian language, the region was dominated by Aramaic. This language, also Semitic, was introduced by the Assyrian empire and spread throughout the region. It remained dominant until the rise of Islam in the 7th century CE.
Today, the primary language of southern Mesopotamia is Arabic. This is a result of the Arab conquests of the 7th century and the subsequent dominance of Arabic culture and language.
It's important to note that:
* Ancient Sumerian was spoken in Mesopotamia before Akkadian, but it was mostly replaced by Akkadian. However, it survived as a liturgical language for a long time.
* Other languages were also spoken in the region throughout history, such as Elamite and Old Persian.
* Various dialects of Arabic are spoken in southern Mesopotamia, along with some Kurdish and Turkic languages.
Therefore, it's difficult to give a simple answer to what language is spoken in southern Mesopotamia, as it depends on the specific time period and the population group being considered.