org-exp: Add japanese translation

* org-exp.el (org-export-language-setup): Add japanese translation.

Translation by Hideki SAITO
<CAAaRP5umR8kDfZoZw6y2XJgyL70YdiJqLtpBvX++0ff+mU=fhA@mail.gmail.com>,
converted to numeric character entities.

TINYCHANGE

lisp/org-exp.el

@@ -192,6 +192,9 @@ This option can also be set with the +OPTIONS line, e.g. \"-:nil\"."
     ("hu" "Szerzõ" "Dátum" "Tartalomjegyzék" "Lábjegyzet")
     ("is" "Höfundur" "Dagsetning" "Efnisyfirlit" "Aftanmálsgreinar")
     ("it" "Autore"     "Data"  "Indice" "Note a piè di pagina")
+    ;; Use numeric character entities for proper rendering of non-UTF8 documents
+    ;; ("ja" "著者"       "日付"  "目次"          "脚注")
+    ("ja" "著者" "日付" "目次" "脚注")
     ("nl" "Auteur"     "Datum" "Inhoudsopgave" "Voetnoten")
     ("no" "Forfatter"  "Dato"  "Innhold" "Fotnoter")
     ("nb" "Forfatter"  "Dato"  "Innhold" "Fotnoter")  ;; nb = Norsk (bokm.l)