Final answer:
The language usually set to music in a madrigal was Italian, which was a popular form of secular vocal music during the Renaissance.
Step-by-step explanation:
In Renaissance music, the language of the poem set to music in a madrigal was usually Italian. The Italian madrigal became one of the most prominent secular genres during this era. Madrigals were typically set to short love poems and were characterized by their emotional depth and complex vocal polyphony.
The prominence of the madrigal in secular music alongside other forms like the French chanson and the Spanish villancico underlines the diversity of expressive forms that emerged during the Renaissance period. The Italian madrigal was highly influential and later spread to other European countries, including England, adapting to the local languages and tastes.