搞了一周了，不知道问题是出在Language*.properties文件上还是portlet的配置文件上。
2011-08-03 14:34:03,562 ERROR [http-8888-Processor24] com.liferay.taglib.util.IncludeTag - Current URL

/c/portal/render_portlet generates exception: Can't find resource for bundle

com.liferay.portlet.PortletResourceBundle, key javax.portlet.title
2011-08-03 14:34:03,562 ERROR [http-8888-Processor24] com.liferay.taglib.util.IncludeTag -

java.util.MissingResourceException: Can't find resource for bundle

com.liferay.portlet.PortletResourceBundle, key javax.portlet.title
at java.util.ResourceBundle.getObject(ResourceBundle.java:384)
at java.util.ResourceBundle.getString(ResourceBundle.java:344)
at com.liferay.portal.util.PortalImpl.getPortletTitle(PortalImpl.java:1975)
at com.liferay.portal.util.PortalUtil.getPortletTitle(PortalUtil.java:601)
at com.liferay.portal.util.comparator.PortletTitleComparator.compare

(PortletTitleComparator.java:62)
at com.liferay.portal.util.comparator.PortletTitleComparator.compare

(PortletTitleComparator.java:42)
at java.util.Arrays.mergeSort(Arrays.java:1270)
at java.util.Arrays.mergeSort(Arrays.java:1282)
at java.util.Arrays.sort(Arrays.java:1210)
at java.util.Collections.sort(Collections.java:159)
at com.liferay.portal.kernel.util.ListUtil.sort(ListUtil.java:185)

<!--liferay-display.xml-->
<?xml version="1.0"?>
<!DOCTYPE display PUBLIC "-//Liferay//DTD Display 5.2.0//EN" "http://www.liferay.com/dtd/liferay-display_5_2_0.dtd">

<display>
	<category name="category.sample">
		<portlet id="training-management" />
	</category>
</display>


<!--liferay-portlet.xml-->

<?xml version="1.0"?>
<!DOCTYPE liferay-portlet-app PUBLIC "-//Liferay//DTD Portlet Application 5.2.0//EN" "http://www.liferay.com/dtd/liferay-portlet-app_5_2_0.dtd">

<liferay-portlet-app>
	<portlet>
		<portlet-name>training-management</portlet-name>
		<instanceable>false</instanceable>
		<render-weight>0</render-weight>
	</portlet>
	<role-mapper>
		<role-name>administrator</role-name>
		<role-link>Administrator</role-link>
	</role-mapper>
	<role-mapper>
		<role-name>guest</role-name>
		<role-link>Guest</role-link>
	</role-mapper>
	<role-mapper>
		<role-name>power-user</role-name>
		<role-link>Power User</role-link>
	</role-mapper>
	<role-mapper>
		<role-name>user</role-name>
		<role-link>User</role-link>
	</role-mapper>
</liferay-portlet-app>


<!--portlet.xml-->

<?xml version="1.0"?>

<portlet-app>
<!-- 
 xmlns="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
	version="2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd http://java.sun.com/xml/ns/portlet/portlet-app_2_0.xsd"
 -->
	<portlet>
		<portlet-name>training-management</portlet-name>
		<display-name>Training Management</display-name>
		<portlet-class>com.portlet.HibernatePortlet</portlet-class>
		<!-- namespace -->
		<init-param>
			<name>viewNamespace</name>
			<value>/trainingmanagement</value>
		</init-param>
		<!--  The default action to invoke in view mode.-->
		<init-param>
			<name>defaultViewAction</name>
			<value>trainingManagement</value>
		</init-param>
		<expiration-cache>0</expiration-cache>
		<supports>
			<mime-type>text/html</mime-type>
		</supports>
		<resource-bundle>com.liferay.portlet.StrutsResourceBundle</resource-bundle>
		<security-role-ref>
			<role-name>administrator</role-name>
		</security-role-ref>
		<security-role-ref>
			<role-name>guest</role-name>
		</security-role-ref>
		<security-role-ref>
			<role-name>power-user</role-name>
		</security-role-ref>
		<security-role-ref>
			<role-name>user</role-name>
		</security-role-ref>
	</portlet>
</portlet-app>

 Language.properties文件中配置：

javax.portlet.title.training-management=Training Management

category.sample=Sample