Struts supports internationlization by means of key value pairs . Struts Documentation can provide much insight but it is very simple and straightforward to do so .
Actually key values pairs are stored in property files(Resource Bundles) and based on locale these bundles are picked up . Struts gives that implementation .
You can also look into java.util.ResourceBundle that will give you fair enough idea.
Locales are like en_US , fr_FR means US english , French France etc .
One imp point though if your app needs to be a true i118n compliant you need to support UTF-8 charset . This charset can be set in META tag of
JSP and on the server side it is taken care by App Servers .
On the DB side again while installing the DB and making an instance you need to specify the charset to UTF8 ....
This will ensure that all requests are coming in UTF-8 and all DB data is again in UTF-8 .
Hope it helps
-nikhil