By default, the capability to sense the browser locale setting is enabled in JSTL. This means that the client determines (through its browser setting) which locale to use, and allows page authors to cater to the language preferences of their clients.
You can set the resource bundle at runtime with the JSTL fmt:setBundle and fmt:bundle tags. fmt:setBundle is used to set the localization context in a variable or configuration variable for a specified scope. fmt:bundle is used to set the resource bundle for a given tag body.
The message tag is used to output localized strings. The following tag from tut-install/javaeetutorial5/examples/web/bookstore4/web/books/bookcatalog.jsp is used to output a string inviting customers to choose a book from the catalog.
The param subtag provides a single argument (for parametric replacement) to the compound message or pattern in its parent message tag. One param tag must be specified for each variable in the compound message or pattern. Parametric replacement takes place in the order of the param tags.