setting i18n property to true for a document brakes the text layout.

Compile and run the next test:

public class I18nTest {
    public static void main(String[] args) throws Exception {
        JFrame jFrame = new JFrame();
        JEditorPane component = new JEditorPane();
        component.setEditorKit(new StyledEditorKit());
        component.getDocument().putProperty("i18n", Boolean.TRUE);
        SimpleAttributeSet attrs = new SimpleAttributeSet();
        StyleConstants.setFontSize(attrs, 72);
        StyleConstants.setBold(attrs, true);
        StyleConstants.setUnderline(attrs, true);
        component.getDocument().insertString(0, "test test", null);
        component.getDocument().insertString(5, "TEST TEST TEST", attrs);
        jFrame.getContentPane().add(new JScrollPane(component));
        jFrame.setSize(300, 500);
        jFrame.setVisible(true);
    }
}

it produces layout shown on the l2.png screenshot, but should look like l1.png.