Complex sentence: From Metatarsus the two Gauls learn that he had just been celebrating with Goldendelicius in a nearby tavern for Goldendelicius'promotion as Caesar's personal slave, and that Caesar is about to make a triumph the very next day for his victory over the pirates.
Split into simpler sentences: From Metatarsus the two Gauls learn that he has just been celebrating with Goldendelicius in a nearby tavern. Goldendelicius has been appointed as Caesar's personal slave, and Caesar himself is due to hold a triumph the very next day for his victory over the pirates.