fix i18n messages when token is 0

static/app-strings.json

@@ -929,4 +929,4 @@
   "Use custom wallet servers": "Use custom wallet servers",
   "Remove custom wallet server": "Remove custom wallet server",
   "Add": "Add"
-}
+}

ui/i18n.js

@@ -59,6 +59,6 @@ export function __(message, tokens) {
   }
 
   return translatedMessage.replace(/%([^%]+)%/g, function($1, $2) {
-    return tokens[$2] || $2;
+    return tokens.hasOwnProperty($2) ? tokens[$2] : $2;
   });
 }