add ja-JP (Japanese) translation

src/lib/i18n/locales/languages.json

@@ -35,6 +35,10 @@
         	"code": "it-IT",
         	"title": "Italian"
     	},
+	{
+    		"code": "ja-JP",
+    		"title": "Japanese"
+	},
 	{
     		"code": "pt-PT",
     		"title": "Portuguese (Portugal)"