In additions to component attributes and ZUML attributes, you could handle browser and Locale dependent resource programmingly in Java. Here are a list of methods that you could use.
The encodeURL, forward, and include methods in org.zkoss.zk.ui.Exection for encoding URL, forwarding to another page and including a page. In most cases, these methods are all you need.
The locate, forward, and include method in org.zkoss.web.servlet.Servlets for locating Web resouces. You rarely need them when developing ZK applications, but useful for writing a servlet, portlet or filter.
The encodeURL method in org.zkoss.web.servlet.http.Encodes for encoding URL. You rarely need them when developing ZK applications, but useful for writing a servlet, portlet or filter.
The locate method in org.zkoss.util.resource.Locators for locating class resources.