Flutter - Character encoding is not behaving as expected - flutter

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.