In which language were most inscriptions on copper plates written which recorded the donation of land grants by kings in ancient India?

Sanskrit

Since ancient times, land grants have been prevalent, and many of these were documented in inscriptions. While some inscriptions were etched on stone, the majority were inscribed on copper plates. These copper plates likely served as official records of the land grants bestowed upon recipients. The surviving records primarily pertain to grants made to religious institutions or Brahmanas. The inscriptions were predominantly written in Sanskrit, though in certain instances, especially from the seventh century onwards, they featured a combination of Sanskrit and a local language like Tamil or Telugu.