Platform: Solaris 11, Redhat Linux 5
locale: Arabic and Hebrew
build: 6u10 b21.

This problem exists since 1.4.2_17.

To reproduce the bug:
Choose Solaris or Redhat Linux platform.
1. Install jdk6u10 b21
2. Install test tools GS-Tonga_12.zip
3.Set test environment
4. run runnit.sh script: sh runnit.sh -keywords:"ar&&manual"
5. Follow to JMenuItemTest. Change LAF to GTK+ from LookAndFeel menu. Click "TestMenu". Then focus mouse to "Radio Button Menu Item" of right-to-left menuitem.
6. Note "Alt-1" , the word has been truncated.

Or compiled and run the application separately: i18n_mustang_ws\i18n\src\GS-Manual\ComponentOrientationTest\JMenuItemTest.java
I have compiled and archived it as JMenuItemTest.jar in attachment. Execute "$JAVA_HOME/bin/java -jar JMenuItemTest.jar" to reproduce the bug:
1. Execute "$JAVA_HOME/bin/java -jar JMenuItemTest.jar"
2. Change LAF to GTK+ from LookAndFeel menu. Click "TestMenu". Then focus mouse to "Radio Button Menu Item" of right-to-left menuitem.
3. Note "Alt-1" , the word has been truncated.

src.zip file is source code of JMenuItemTest.jar in attachemt.
I can reproduce this in any locale. So, it's not specific to Arabic/Hebrew. But it looks like related to rendering or layout related to right-to-left component-orientation and/or gtk, shown by the following part of the code:

  menu.add(menuItem);
        menuItem = new JRadioButtonMenuItem("Radio Button Menu Item");
        menuItem.setComponentOrientation(o);
        menuItem.setSelected(true);
        menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_1,
                                                       ActionEvent.ALT_MASK));
Also, the RadioButton looks like a checkbox in this test case in all 3 look and feels.