Tested on RedHat EL 4, ja_JP.UTF-8 locale. Following exception was thrown and jconsole didn't start.

# jconsole
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.initSystemColorDefaults(GTKLookAndFeel.java:1258)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.loadStyles(GTKLookAndFeel.java:1500)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.access$000(GTKLookAndFeel.java:37)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel$WeakPCL$1.run(GTKLookAndFeel.java:1440)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160) at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.initSystemColorDefaults(GTKLookAndFeel.java:1258)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.loadStyles(GTKLookAndFeel.java:1500)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel.access$000(GTKLookAndFeel.java:37)
        at com.sun.java.swing.plaf.gtk.GTKLookAndFeel$WeakPCL$1.run(GTKLookAndFeel.java:1440)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)

Worked fine in C locale.
Exception also occurs in Solaris, but jconsole itself starts in that case.