How to insert a placeholder in a json key:value ? Flutter - flutter

Question

I'm porting my Swift app to Flutter and for localising it I'm following this https://github.com/billylev/flutter_localizations but I can't see how to insert placeholder to insert a value in the translated values.
Basically the guide uses
String text(String key) {
return _localisedValues[key] ?? "$key not found";
}
to get the corresponding key:value pair from a .json file as
{
"Shop": "Negozio",
}
I just pass it in the Textwidget as :
Text(AppLocalizations.instance.text('Shop')).
How to modify text to insert one or more placeholders and how would be the .json be constructed?
Say for the value "User": "User" I'd like to insert a value after the transaction I can simply use a string sum and add the value as `Text(
AppLocalizations.instance.text('User') + ' ${widget.user.name}', but if I need to insert a value in the middle of the translated sentence, eg a message, I don't see how to accomplish it.
I need it to make localised versions of incoming push notification, and they have args.
In Swift I have it like this:
"ORDER_RECEIVED_PUSH_TITLE" = "Order number: %#";
"ORDER_RECEIVED_PUSH_SUBTITLE" = "Shop: %#";
"ORDER_RECEIVED_PUSH_BODY" = "Thank you %#! We received your order and we'll let you know when we start preparing it and when it's ready. Bye";
Any suggestions on how to accomplish that in Flutter?
Many thanks

Answer 1

I was suggested this package https://pub.dev/packages/sprintf#-installing-tab- and it works just as I needed. Sprintf just lets you specify one or more placeholders in a String and pass an array of args.
https://developermemos.com/posts/using-sprintf-flutter-dart. for more info, even this is pretty much it. So for example
"ORDER_RECEIVED_PUSH_TITLE" = "Order number: %#";
in the .json file would be :
{
"ORDER_RECEIVED_PUSH_TITLE": "Oder number: %s"
}
and using it would be
String orderNumber = 'some uuid';
Text(Sprintf(AppLocalitazions.instance.text('ORDER_RECEIVED_PUSH_TITLE'),[orderNumber]);
Hope this helps others.