Complex sentence: It was spoken by a Gallo-Belgic tribe called the Érainn (in Irish), Iverni (in Latin), and Firbolg (in the Irish Book of Invasions).
Split into simpler sentences: It was spoken by a Gallo-Belgic tribe called the Érainn (in Irish) or Iverni (in Latin). They have been linked with the Firbolg (in the Irish Book of Invasions).