Complex sentence: Two manuscripts are known to have existed, both dated to the late 16th century and written respectively in Italian and in Spanish--although the Spanish manuscript is now lost, its text surviving only in a partial 18th-century transcript.
Split into simpler sentences: Two manuscripts are known to have existed, both dated to the late 16th century, with one written in Italian and the other in Spanish. The Spanish manuscript is now lost, its text surviving only in a partial 18th-century transcript.