According to this example - http://books.zkoss.org/wiki/ZK_Developer%27s_Reference/Internationalization/Labels#Use_labels
If you use the method of "org.zkoss.util.resource.Labels.reset();" to clear the cache, the labels instance still keeps the old value.

For example,

Test.zul,

<button label="${labels.title}" onClick='org.zkoss.util.resource.Labels.reset();Executions.sendRedirect("")'/>

i3-label.properties

title=Test