#!/bin/bash

export LOCPATH=$HOME/.wine/locale-ja/
mkdir -p $LOCPATH
localedef -f EUC-JP -i ja_JP $LOCPATH/ja_JP.EUC-JP
localedef -c -f SHIFT_JIS -i ja_JP $LOCPATH/ja_JP.SJIS

## You get a warning that SHIFT_JIS is not ASCII compatible, that is normal. With that setup you can now run apps using
# env LOCPATH=$HOME/.wine/locale-ja/ LANG=ja_JP.SJIS wine prog.exe

## or if the app is using EUC-JP (less common afaik)
# env LOCPATH=$HOME/.wine/locale-ja/ LANG=ja_JP.EUC-JP wine prog.exe