translation-ja: add ja to the language list; add author name

Author: wtsnjp

AUTHORS.md

@@ -26,4 +26,4 @@ The following people have made contributions to learnlatex.org:
 - Dung Vu
 - Uwe Ziegenhagen
 - निरंजन
-
+- Takuto Asakura

_config.yml

@@ -68,6 +68,12 @@ defaults:
     values:
       lang: "fr"
       label: "Français"
+  -
+    scope:
+      path: "ja"
+    values:
+      lang: "ja"
+      label: "日本語"
   -
     scope:
       path: "pt"
@@ -97,4 +103,4 @@ defaults:
       path: "ca"
     values:
       lang: "ca"
-      label: "Català"
+      label: "Català"