If you want to take advantage of HST-2 Repository Dynamic ResourceBundle as MessageSource in your Spring Framework application, then you should configure the following MessageSource bean instead of the default ResourceBundleMessageSource.
<beans>
<!-- SNIP -->
<!-- Set HstRepositoryResourceBundleMessageSource to be able to use HST-2 Repository Dynamic Resource Bundles. -->
<bean id="messageSource" class="org.onehippo.forge.hst.spring.support.HstRepositoryResourceBundleMessageSource">
<!--
You don't have to specify hard-coded 'basenames' property here,
but you can still add some standard Java resource bundle basenames additionally.
So, in this example, if a resource key is not found from the bundle(s) configured in
HST-2 configuration (hst:sitemapitem, hst:mount, hst:virtualhost or hst:virtualhosts as ordered by precedence), then it may fall
back to the specified Java standard resource bundle (e.g, 'classpath:org/hippoecm/hst/demo/spring/webmvc/exceptions_en.properties').
-->
<property name="basenames">
<list>
<value>org.hippoecm.hst.demo.spring.webmvc.exceptions</value>
</list>
</property>
</bean>
<!-- SNIP -->
</beans>
See the Javadoc of HstRepositoryResourceBundleMessageSource for more detail.