Theodor Fontane ( ; December 30 , 1819 â `` September 20 , 1898 ) was a German novelist and poet , regarded by many to be the most important 19th-century German-language realist writer . Theodor Fontane ( ; 30 December 1819 â `` 20 September 1898 ) was a German novelist and poet , regarded by many as the most important 19th-century German-language realist writer .