it's due to the fact that most Japanese devs still have no clue about achievements.
Many achievements have CERTAIN numerical quota requirements, and western devs tend to put the actual numbers on them.
e.g
Achievement = Headshot Master - 20G
western dev description - Get 50 headshots with the sniper rifle
japanese dev description - Hey! Shooting people is fun! Keep trying to hit them in the head.
seriously. I'm playing Tales of Vesperia atm and all the cheevs have vague descriptions.