struts.custom.i18n.resources=languages_actions,languages_views

This definition instructs struts to use the files languages_actions.properties and languages_view.properties for your language definitions. When there is a new request locale, such as zh_CN (chinese), struts will find for the file languages_actions_zh_CN.properties, or if defaults to en_US (english), struts will use the file language_actions_en_US.properties.
On top of that, there can be many places where language definitions can be found. They will be searched in the following order:

1. ActionClass.properties
2. BaseClass.properties (all the way to Object.properties)
3. Interface.properties (every interface and sub-interface)
4. ModelDriven’s model (if implements ModelDriven), for the model object repeat from 1
5. package.properties (of the directory where class is located and every parent directory all the way to the root directory)
6. search up the i18n message key hierarchy itself
7. global resource properties

I put my files in the main WEB-INF\classes folder where struts.properties can be found
Read here for more information on how struts 2 searches for i18n definitions.

user.submit.image=/images/en_US/submit.gif
user.welcome=Welcome, {0}
user.link=<a href="somelink.action?id={1}&amp;token={2}">{0}</a>' document
user.validation.token.invalid={0} does not exists in the system

the above is an example of a en_US language definition file. You can see how the image and welcome message would be different in a zh_CN language definition file. but just for the heck of it, here it is anyway

user.submit.image=/images/zh_CN/submit.gif
user.welcome={0}, 你好
user.link=<a href="somelink.action?id={1}&amp;token={2}">{0}</a> 的文件
user.validation.token.invalid={0} 不纯在于系统

The key here in flexibility is the use of # parameters for the definitions (very printf-ish). This allows the dynamic data to be reformatted to any language structure (left to right, right to left, orientation of grammer, verbs, subject, topics, etc). Really smart way to do it!

<%@ page contentType="text/html; charset=UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<h1><s:text name="user.welcome">
	<s:param value="user.name" />
</s:text></h1>
<s:text name="user.link">
	<s:param value="document.name" />
	<s:param value="document.id" />
	<s:param value="document.token" />
</s:text>
<form input="">
	<s:submit type="image" src="%{getText('user.submit.image')}" cssClass="submit" />
</form>

Or in Java,

public class SomeActions extends ActionSupport {
	public String someMethod() throws Exception {
		if (!token.equalsIgnoreCase("abcdefghi")) {
			String [] messageargs = { token };
			addActionError(getText("user.validation.token.invlaid", messageargs));
		}
	}
 
	private String token;
	public String getToken() 	{ return  token; }
	public void setToken(String s) 	{ token = s; }
}

The above examples goes to show how you can combine dynamic data with the i18n strings in a JSP or a Java file