Added japanese translation. Many thanks to HORIUCHI Takahiko for the translation.

interface/lib/lang/ja.lng

interface/web/admin/lib/lang/ja.lng

interface/web/admin/lib/lang/ja_firewall.lng

interface/web/admin/lib/lang/ja_firewall_list.lng

interface/web/admin/lib/lang/ja_groups.lng

interface/web/admin/lib/lang/ja_groups_list.lng

interface/web/admin/lib/lang/ja_language_add.lng

interface/web/admin/lib/lang/ja_language_complete.lng

interface/web/admin/lib/lang/ja_language_edit.lng

interface/web/admin/lib/lang/ja_language_export.lng

interface/web/admin/lib/lang/ja_language_import.lng

interface/web/admin/lib/lang/ja_language_list.lng

interface/web/admin/lib/lang/ja_remote_user.lng

interface/web/admin/lib/lang/ja_remote_user_list.lng

interface/web/admin/lib/lang/ja_server.lng

interface/web/admin/lib/lang/ja_server_config.lng

interface/web/admin/lib/lang/ja_server_config_list.lng

interface/web/admin/lib/lang/ja_server_ip.lng

interface/web/admin/lib/lang/ja_server_ip_list.lng

interface/web/admin/lib/lang/ja_server_list.lng