The entry in your struts-config.xml file is incorrect.
You should not create separate entries for each language, but only one entry for the entire bundle.
Struts will then select the correct properties file based on the user's preferred language set in the browser.
For example, suppose you want to support English, Italian, and Spanish. You would create the following files in WEB-INF/classes/example:
ApplicationResources.properties (the default in case the locale cannot be determined)
ApplicationResources_en.properties (english)
ApplicationResources_es.properties (spanish)
ApplicationResources_it.properties (italian)
The entry in your struts-config.xml file would simply be:
<message-resources parameter="example.ApplicationResources" />
The message-resources stanza in struts-config.xml identifies only the base name of the bundle. It not language specific.
Struts then picks the language based on the preferred language set in the user's browser. If you want the user to be able to select the language, then you can set the locale programatically by using the setLocale() method in the Action class.
This link explains struts messages in greater detail. I'd strongly recommend you read it.