Complex sentence: In 1779 he entered the French military service with the Royal-Bavière Regiment, accompanied General Rochambeau to America as one of his his adjutants and also acted as an interpreter between Rochambeau and Washington.
Split into simpler sentences: In 1779 he entered the French military service with the Royal-Bavière Regiment. He accompanied the French commander in chief General Rochambeau to America and also acted as an interpreter between Rochambeau and Washington.