Flutter - Character encoding is not behaving as expected

Question

I am parsing a local JSON file that has words containing rarely used special characters in Icelandic.

When displaying the characters I get mixed up symbols but not the characters, for some others I just get a square instead of a symbol.

I am using this type of encoding "\u00c3"

Update: Example of the characters I am using: þ, æ, ý, ð

Q: What is the best way to display those kind of characters and avoid any chance of display failures?

Update #2: How I am parsing:

Future<Null> getAll() async{
    var response = await 
    DefaultAssetBundle.of(context).loadString('assets/json/dictionary.json');
    var decodedData = json.decode(response);
    setState(() {
      for(Map word in decodedData){
        mWordsList.add(Words.fromJson(word));
      }
    });
  }

The class:

class Words{
  final int id;
  final String wordEn, wordIsl;

  Words({this.id, this.wordEn, this.wordIsl});

  factory Words.fromJson(Map<String, dynamic> json){
    return new Words(
      id: json['wordId'],
      wordEn: json['englishWord'],
      wordIsl: json['icelandicWord']
    );
  }
}

JSON Model:

{
    "wordId": 47,
    "englishWord": "Age",
    //Here's a String that has two special characters
    "icelandicWord": "\u00c3\u00a6vi"
}

Answer 1

I had similar issues with accented characters. They were not displayed as expected. This worked for me

final codeUnits = source.codeUnits;
return Utf8Decoder().convert(codeUnits);

Answer 2

The problem is that your JSON is stored locally.

Let's say you have
Map<String, String> jsonObject = {"info": "Æ æ æ Ö ö ö"};

So to show your text correctly you have to encode and decode back your JSON with utf-8.

I understand that's serialization and deserialization are costly operations, but's it's a workaround for locally stored JSON objects that contains UTF-8 texts.

import 'dart:convert';
jsonDecode(jsonEncode(jsonObject))["info"]

If you get that JSON from server, then it's much more simpler, for example in dio package you can chose contentType params that's is "application/json; charset=utf-8" by default.