ADDITIONAL SYSTEM INFORMATION :
Mac OS 15.3, Java SE 11.*, JDK 22.*, OpenJDK 11.*...
Bug not present on Windows and Linux

A DESCRIPTION OF THE PROBLEM :
While Locale.getDefault() returns "fr_BE", Swing components remain in English. However, some Locale's are working correctly, such as Locale.GERMANY (correct translation of buttons and other components)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See test case below

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The buttons and other Swing components should be translated in French when Locale.setDefault(Locale.FRANCE) is called.
ACTUAL -
Components are correctly translated when Locale.setDefault(Locale.GERMANY) is called but not when Locale.setDefault(Locale.FRANCE) is called.

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import java.util.Locale;
import javax.swing.JOptionPane;

public class Test {
public static void main(String[] args) {

System.out.println(Locale.getDefault());

Locale.setDefault(Locale.FRANCE); // Doesn't work
//Locale.setDefault(Locale.GERMANY); // Works !

JOptionPane.showConfirmDialog(null, "Default locale: " + Locale.getDefault());
}

}

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