Part of the reason why WW2 didn't spark the same level of anti-German backlash is because many who were beginning their political careers during WW1 were horrified at the anti-German bigotry that arose during WW1; and thus when WW2 came around, made sure to portray the WW2 German government as tyrannizing the German people, rather than synonymous with them.
Apparently, though, that wasn't a concern for Japanese-Americans, who got to 'enjoy' the weight of US 1940s racism.