Migrate to JSON i18n

Procedure per https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php
with shim.

Change-Id: Ied3a4c392cf2ea16c6e858a1baaf9790db95e1f4

i18n/ja.json

@@ -0,0 +1,24 @@
+{
+    "@metadata": {
+        "authors": [
+            "Aotake",
+            "Fryed-peach",
+            "JtFuruhata",
+            "Schu",
+            "Shirayuki"
+        ]
+    },
+    "contributionscores": "貢献得点",
+    "contributionscores-desc": "ウィキデータベースへの[[Special:ContributionScores|貢献度が高い利用者]]の統計",
+    "contributionscores-info": "得点では、編集したページ数を主に評価し、さらに編集回数の多さにも配慮します。",
+    "contributionscores-top": "(上位$1名)",
+    "contributionscores-days": "{{PLURAL:$1|最近1日|最近$1日間}}",
+    "contributionscores-allrevisions": "すべての期間",
+    "contributionscores-score": "得点",
+    "contributionscores-rank": "順位",
+    "contributionscores-pages": "ページ数",
+    "contributionscores-changes": "編集回数",
+    "contributionscores-username": "利用者名",
+    "contributionscores-invalidusername": "無効な利用者名",
+    "contributionscores-invalidmetric": "無効な尺度"
+}