The main language used in the Mauryan court and administration was Prakrit.
Prakrit was not one single standardized language but a group of Middle Indo-Aryan languages and dialects related to Sanskrit. During the Mauryan period, these forms were widely understood and suited to communication across a large and diverse empire. Ashoka’s inscriptions, issued in the 3rd century BCE, provide the clearest surviving evidence of this administrative language policy.
Most of Ashoka’s edicts were written in regional varieties of Prakrit using the Brahmi script. In the northwest, some inscriptions used related languages and different scripts, including Aramaic and Greek. This regional variation shows that Mauryan administration adapted its public communications to local audiences rather than relying on one uniform linguistic system.
Sanskrit was an important learned language, but it was not generally the main language of Mauryan public administration. Pali is closely related to Prakrit and is strongly associated with Buddhist literature, yet it is not the best answer to this question. Tamil was prominent in the far south but was outside the Mauryan administrative core.