I can make it works when using device_preview and getx GetMaterialApp. GetMaterialApp can perfectly works with device_preview on many things such as size, orientation etc. GetMaterialApp.router is not the case. I found that locale changes in device_preview can’t propagate to GetMaterialApp.router. I raised a issue, however getx has a bad reputation on fixing issues. I can’t wait so long and I sought other options. Things I tried was to use GetMaterialApp, however always to get several errors.

void main() => runApp( DevicePreview( enabled: !kReleaseMode, builder: (context) => MyApp(), // Wrap your app ), ); class MyApp extends StatelessWidget { final botToastBuilder = BotToastInit(); @override Widget build(BuildContext context) { return GetMaterialApp.router( useInheritedMediaQuery: true, locale: DevicePreview.locale(context), builder: (context, child) { child = DevicePreview.appBuilder(context, child); child = botToastBuilder(context, child); return child; }, theme: ThemeData.light(), darkTheme: ThemeData.dark(), home: const HomePage(), ); } } Reference: https://pub.dev/packages/bot_toast https://stackoverflow.