Queen Isabella I of Castile primarily spoke Spanish. However, it is important to note that during her time in the late 15th century, the Spanish language was not as standardized as it is today. Therefore, her dialect would have included various regional influences.
Additionally, Isabella was born into a noble family and received an education typical of aristocrats of her time, which included knowledge of Latin, the language of the Church, and some understanding of other languages that were prevalent in the courts of Europe, such as French. Nevertheless, her primary and most utilized language in governance and daily life was Spanish.
Isabella’s language played a crucial role during her reign, especially as she collaborated with her husband, Ferdinand II of Aragon, to unite Spain. Their joint efforts in the Reconquista and the promotion of exploration led to significant historical developments, all conducted in the Spanish language.