Complex sentence: In 1907 he left for Paris, where he continued to school his voice then in 1908--1918 performed at London's Covent Garden and Berlin's Komische Oper.
Split into simpler sentences: In 1907 he left for Paris where he continued in schooling his voice. In 1908--1918 he performed at London's Covent Garden and at Berlin's Komische Oper.