On Some Android device Default locale and System locale are different.

On Some Android device (for example Samsung S10) Default locale and system locale name prints different if language settings has been chosen which says in note "May not be available in some apps" (attached screenshot)

Steps:

Go to 'Language settings'

• Choose a language that has a note "May not be available in some
  apps" (e.g. Russian)
• Print Following code snippet in main :

  qDebug()<<QLocale::system().name(); // prints "en_US"
  qDebug() << QLocale().name(); //"en_US"
  qDebug() << locale.uiLanguages().at(0); //"el-CY"