The Capitals drafted Forsberg in the first round last summer with the No. 11 pick. The 18-year-old is in his second season with the Leksands IF of the Swedish Elite League where he has eight goals and nine assists in 43 games this season.
Erat, meanwhile, is leaving the only NHL club he has ever played for.
Erat has four goals and 21 points in 36 games this season for Nashville. The 31-year-old Czech is second on the Predators' all-time list in career points (481), goals (163) and assists (318).
His best season came last year when he reached 19 goals and 39 assists, eclipsing the 50-point plateau for the fifth time in his last six seasons.
He has played all 723 of his career NHL games with Nashville after the Preds drafted him in the seventh round in 1999.
Latta, who hails from St. Clements, Ont., has scored nine goals and 35 points in 67 games this season for the American Hockey League's Milwaukee Admirals.
He was a third round pick by Nashville in the 2009 draft and is expected to report to Washington's AHL affiliate in Hershey.