Flutter mqtt - Unicode(Korean) doesn't work - flutter

Question

I am using mqtt_client: ^9.6.8 in my flutter project.
I want to subscribe to Korean topics, like topic: "test/안녕"
I want to get messages in Korean, like message: "안녕하세요"
currently if I try to subscribe to a korean topic, the client disconnects and the process just kills itself.
The log was a little bit different before, but this is the current log after I subscribe to a korean topic.
I/flutter (18972): 1-2022-08-09 15:38:40.135206 -- MqttConnectionBase::_onDone - calling disconnected callback
I/flutter (18972): 1-2022-08-09 15:38:40.135985 -- MqttConnectionKeepAlive::stop - stopping keep alive
I/flutter (18972): EXAMPLE::OnDisconnected client callback - Client disconnection
I/flutter (18972): EXAMPLE::OnDisconnected callback is unsolicited or none, this is incorrect - exiting
D/HostConnection(18972): createUnique: call
F/libc (18972): FORTIFY: pthread_mutex_lock called on a destroyed mutex (0xb400006dd36425a0)
D/HostConnection(18972): HostConnection::get() New Host Connection established 0xb400006de3607310, tid 19012
F/libc (18972): Fatal signal 6 (SIGABRT), code -1 (SI_QUEUE) in tid 19013 (1.raster), pid 18972
if I send a korean message, then it comes like HÅU± which is not what I want.
I tried to decode with utf8 but I can't seem to do it correctly.
Any helps on this? thanks for every suggestion!!
--edit--
this is the part where I print the received mqtt message
client.updates!.listen((List<MqttReceivedMessage<MqttMessage?>>? c) {
final recMess = c![0].payload as MqttPublishMessage;
final pt =
MqttPublishPayload.bytesToStringAsString(recMess.payload.message);
context.read<SubTopic>().newTopic(c[0].topic);
context.read<SubMessage>().newMessage(pt);
print('Notification: topic is <${c[0].topic}>, payload is <$pt>');
});
this is where I subscribe to the topic
try {
await client.connect();
} on NoConnectionException catch (e) {
print('EXAMPLE::client exception - $e');
client.disconnect();
} on SocketException catch (e) {
print('EXAMPLE::socket exception - $e');
client.disconnect();
}
if (client.connectionStatus!.state == MqttConnectionState.connected) {
print('EXAMPLE::Mosquitto client connected');
for (String topic in _subTopicList) {
print(topic);
client.subscribe(topic, MqttQos.exactlyOnce);
}
} else {
print(
'EXAMPLE::ERROR Mosquitto client connection failed - disconnecting, status is ${client.connectionStatus}');
client.disconnect();
// exit(-1);
}