public class ClientSession extends AbstractClientSession {
  public static final String PREF_USER_LOCALE = "PREF_USER_LOCALE";
  
  ...

  @Override
  protected void execLoadSession() {
    initializeSharedVariables();

    // The locale needs to be set before the Desktop is created.
    String localeString = ClientUIPreferences.getClientPreferences(ClientSession.get()).get(PREF_USER_LOCALE, null);
    if (localeString != null) {
      Locale userLocale = LocaleUtility.parse(localeString);
      setLocale(userLocale);
    }

    setDesktop(new Desktop());
  }
}