LOUISVILLE — Japanese racing has become a consistent presence at the Kentucky Derby over the last decade, but the visitors remain shrouded in mystery. Their horses are kept in detention barns at Churchill Downs for health reasons, surrounded by a forbidding chain-link fence that bears a USDA sign reading “ISOLATION” in bold letters. They bring their own language, own jockeys, own trainers and own way of doing things to Louisville. They’ve been lost in translation, and have lost all attempts to win the Derby. Eight Japan-based horses have run the race, seven of them in the last 10 years, with none finishing better than third. (A notable third, which we’ll get to.) The average finish has been 10th. But the racing world is largely in agreement that a Japanese Derby victory is inevitable. The country’s racing industry has invested too much, too wisely, for too long to be denied.…