Special Characters are Replaced with a Square
Problem
My file was created with another application and it contains special characters (such as é, ©, ®, etc.) but Oxygen JSON Editor displays a square for these characters.
Solution
You must set a font that is able to render the special characters in the Font preferences. If it is a text file, you must also set the encoding used for non XML files. If you want to set a font that is installed on your computer but that font is not accessible in the Font preferences, this means the Java virtual machine is not able to load the system fonts (probably because it is not a True Type font). It is a problem of the Java virtual machine and a possible solution is to copy the font file in the [JVM_DIR]/lib/fonts folder. [JVM_DIR] is the value of the property java.home that is available in the System properties tab of the About dialog box that is opened from menu .