In Lost in Translation, we see a picture of the actor in the waning years of his career struggling to find money. Bill Murray's character's decision to go to Japan and act in whiskey commercials is seen as the bottom of the barrel: his name is for sale to anybody.
What isn't addressed in the movie is that the practice of English-speaking celebrities acting in Japanese commercials is fairly common. Japander.com maintains a huge collection of these commercials, featuring many famous actors and other celebrities from the past twenty or twenty five years in commercials for all sorts of Japanese products.
Think about it this way: you are offered a lot of money to be flown to Japan, act in a short commercial, and come home. The odds of any of your English-speaking fans seeing your commercial are practically nil. Without resources like Japander, nobody would ever really find out.
In fact, plenty of celebrities have acted in commercials for Suntory Whiskey, which Harris is advertising in the movie. Among them are Francis Ford Coppola (whose commercial was made by Akira Kurosawa, no less) and Sean Connery. Coppola's stint in Japanese commercials was partially the inspiration for Lost in Translation (Sophia Coppola is his daughter), and Connery's participation is indirectly referenced through the Bond actor discussion that Harris has during the filming of the commercial.
You can also take a look at Nicolas Cage's TV Commercial for Pachinko.