Why is my JSON file not saved in UTF-8 after editing?

Question

How can edit a .json file with all special characters and save it in UTF-8 in an automatic way. (.properties files and similar)

I've tried (How to open file in UTF-8 format in Netbeans; without distorting characters?, How to change file encoding in NetBeans?)

• -J-Dfile.encoding=UTF-8 In default options but that isn't working to me
• Open this file with gedit notepad and others and save it with encode utf8
• Right click > Properties > Sources > encode: utf8

Note: My project is already configured with UTF8 by default.

File editing

{
    "LOGIN": "Iniciar sesión",
    "PASSWORD": "Contraseña",
    "RECOVER_PASSWORD": "Recuperar contraseña",
    "PASSWORD_OR_EMAIL_INCORRECT": "Contraseña o correo electrónico incorrectos"
}

Saved file

{
    "LOGIN": "Iniciar sesi\u00f3n",
    "PASSWORD": "Contrase\u00f1a",
    "RECOVER_PASSWORD": "Recuperar contrase\u00f1a",
    "PASSWORD_OR_EMAIL_INCORRECT": "Contrase\u00f1a o correo electr\u00f3nico incorrectos"
}