Using Japanese locales on a character based terminal (TTY) requires that you use terminal settings to make line editing work correctly.
If your terminal is a CDE Terminal emulator (dtterm), use stty(1) with argument -defeucw, in any Japanese locale (ja, ja_JP.PCK, or ja_JP.UTF-8). An example in locale ja is:
% setenv LANG ja % stty defeucw
If your terminal is not a CDE Terminal emulator, but the codeset of your terminal is the same as that of the current locale, use this setting, too.
If your terminal's codeset doesn't match that of the current locale, use setterm(1) to enable code conversion. For example, if you are in locale ja but your terminal requires PCK (ShiftJIS code), specify:
% setenv LANG ja % setterm -x PCK
See setterm(1) for details.