title: Dart: Can't access to nested map object
body: <p>I am creating a Flutter application and I can't access to nested map object in <code>dart</code>. 
  My code is as below.</p>
  
  <pre><code> Map&lt;String, String&gt; _localizedValues;
  
    Future&lt;bool&gt; load() async {
      // Load a language JSON file from the 'i18n' folder
      String value = await rootBundle.loadString('i18n/${locale.languageCode}.json');
      Map&lt;String, dynamic&gt; jsonMap = jsonDecode(value);
      _localizedValues = jsonMap.map((key, value) {
        return MapEntry(key, value.toString());
      });
      return true;
    }
  
    String translate(String parent, String key) {
      // Returns a localized text
      return _localizedValues[parent][key];
    }
  </code></pre>
  
  <p>And error occurs <code>[key]</code> this part. It says </p>
  
  <blockquote>
    <p>The argument type 'String' can't be assigned to the parameter type 'int'.</p>
  </blockquote>
  
  <p>JSON file is like this.</p>
  
  <pre><code>{
       "Parent": {
           "key": "key"
       }
   }
  </code></pre>
  
  <p>What am I wrong with this?</p>