How do you enter passwords?
Load up Dream Radar, and start the game. On the Development Lab screen, enter the button combinations accurately, and the password will be complete. There is no specific screen for you to be on whilst entering the password.
Source: I did this myself; experience.
Is the ability of using these passwords for the Japanese copy only?
Actually, no. You may get those Pokemon on the Dream Radar, but note that there are actually two different passwords for each of the different copies, so don't get the English one mixed up with the Japanese one. Here are the English copy's codes:
- Slowpoke: ↑ ↓ → ← Y R L
- Hoothoot: R L Y X ← → Y X
- Beldum: ↑ → ↓ ← X R L
Source: Serebii's list of obtainable Pokemon on Dream Radar.