ox: Add new Japanese translation strings

* lisp/ox.el (org-export-dictionary): Add new Japanese translation
  strings.

A few strings in `org-export-dictionary' didn't have Japanese
translations.  So, I just added.

lisp/ox.el

@@ -5391,6 +5391,7 @@ them."
      ("es" :html "Ecuación" :default "Ecuación")
      ("et" :html "Võrrand" :utf-8 "Võrrand")
      ("fr" :ascii "Equation" :default "Équation")
+     ("ja" :default "方程式")
      ("no" :default "Ligning")
      ("nb" :default "Ligning")
      ("nn" :default "Likning")
@@ -5454,6 +5455,7 @@ them."
      ("es" :default "Indice de Listados de programas")
      ("et" :default "Loendite nimekiri")
      ("fr" :default "Liste des programmes")
+     ("ja" :default "ソースコード目次")
      ("no" :default "Dataprogrammer")
      ("nb" :default "Dataprogrammer")
      ("ru" :html "Список распечаток"
@@ -5465,6 +5467,7 @@ them."
      ("es" :default "Indice de tablas")
      ("et" :default "Tabelite nimekiri")
      ("fr" :default "Liste des tableaux")
+     ("ja" :default "表目次")
      ("no" :default "Tabeller")
      ("nb" :default "Tabeller")
      ("nn" :default "Tabeller")
@@ -5478,6 +5481,7 @@ them."
      ("es" :default "Listado de programa %d")
      ("et" :default "Loend %d")
      ("fr" :default "Programme %d :" :html "Programme %d :")
+     ("ja" :default "ソースコード%d:")
      ("no" :default "Dataprogram %d")
      ("nb" :default "Dataprogram %d")
      ("ru" :html "Распечатка %d.:"
@@ -5489,6 +5493,7 @@ them."
      ("es" :default "vea seccion %s")
      ("et" :html "Vaata peatükki %s" :utf-8 "Vaata peatükki %s")
      ("fr" :default "cf. section %s")
+     ("ja" :default "セクション %s を参照")
      ("ru" :html "См. раздел %s"
       :utf-8 "См. раздел %s")
      ("zh-CN" :html "参见第%s节" :utf-8 "参见第%s节"))
@@ -5545,6 +5550,7 @@ them."
      ("es" :default "referencia desconocida")
      ("et" :default "Tundmatu viide")
      ("fr" :ascii "Destination inconnue" :default "Référence inconnue")
+     ("ja" :default "不明な参照先")
      ("ru" :html "Неизвестная ссылка"
       :utf-8 "Неизвестная ссылка")
      ("zh-CN" :html "未知引用" :utf-8 "未知引用")))