de_DEだから、ただ単純にja_JPにすればいいのかなと思ったら…..「ja」だけで良いのね…
* WordPress Localized Language, defaults to English.
*
* Change this to localize WordPress. A corresponding MO file for the chosen
* language must be installed to wp-content/languages. For example, install
* de_DE.mo to wp-content/languages and set WPLANG to 'de_DE' to enable German
* language support.
*/
define('WPLANG', '');
