The statue is a replica of one which stands in Germany at Worms (pronounced "Verms") according to Wikipedia. (On Worms being pronounced "Verms": I may have gone all through confirmation class, at a Lutheran church, unaware that using the wobbly English 'W' in that name was not quite right).
More photos of the statue and vicinity are below (including one from the 1920s):
Have a look at a map pinpointing Thomas Circle. The Luther Statue is adjacent to it, on the north side.