Each user login session has an associated instance of java.util.Locale (available to the application as a component named locale). Under normal circumstances, you won't need to do any special configuration to set the locale. Seam just delegates to JSF to determine the active locale:

It is possible to set the locale manually via the Seam configuration properties org.jboss.seam.international.localeSelector.language, org.jboss.seam.international.localeSelector.country and org.jboss.seam.international.localeSelector.variant, but we can't think of any good reason to ever do this.

It is, however, useful to allow the user to set the locale manually via the application user interface. Seam provides built-in functionality for overriding the locale determined by the algorithm above. All you have to do is add the following fragment to a form in your JSP or Facelets page:

<h:selectOneMenu value="#{localeSelector.language}">
    <f:selectItem itemLabel="English" itemValue="en"/>
    <f:selectItem itemLabel="Deutsch" itemValue="de"/>
    <f:selectItem itemLabel="Francais" itemValue="fr"/>
</h:selectOneMenu>
<h:commandButton action="#{localeSelector.select}" value="#{messages['ChangeLanguage']}"/>

Or, if you want a list of all supported locales from faces-config.xml, just use:

<h:selectOneMenu value="#{localeSelector.localeString}">
    <f:selectItems value="#{localeSelector.supportedLocales}"/>
</h:selectOneMenu>
<h:commandButton action="#{localeSelector.select}" value="#{messages['ChangeLanguage']}"/>

When this use selects an item from the drop-down, and clicks the button, the Seam and JSF locales will be overridden for the rest of the session.

JSF supports internationalization of user interface labels and descriptive text via the use of <f:loadBundle />. You can use this approach in Seam applications. Alternatively, you can take advantage of the Seam messages component to display templated labels with embedded EL expressions.

Hello=Hello

Hello=G'day

<core:resource-loader>
    <core:bundle-names>
        <value>mycompany_messages</value>
        <value>standard_messages</value>       
    </core:bundle-names>
</core:resource-loader>

<page view-id="/welcome/hello.jsp" bundle="HelloMessages"/>

<h:outputText value="#{messages['Hello']}"/>

<h:outputText value="#{messages.Hello}"/>

Hello=Hello, #{user.firstName} #{user.lastName}

Hello=G'day, #{user.firstName}

@In private Map<String, String> messages;

@In("#{messages['Hello']}") private String helloMessage;

@Name("hello")
@Stateless
public class HelloBean implements Hello {
    @In FacesMessages facesMessages;
    
    public String sayIt() {
        facesMessages.addFromResourceBundle("Hello");
    }
}

There is also a session-scoped instance of java.util.Timezone, named org.jboss.seam.international.timezone, and a Seam component for changing the timezone named org.jboss.seam.international.timezoneSelector. By default, the timezone is the default timezone of the server. Unfortunately, the JSF specification says that all dates and times should be assumed to be UTC, and displayed as UTC, unless a timezone is explicitly specified using <f:convertDateTime>. This is an extremely inconvenient default behavior.

Seam overrides this behavior, and defaults all dates and times to the Seam timezone. In addition, Seam provides the <s:convertDateTime> tag which always performs conversions in the Seam timezone.

Seam applications are also very easily skinnable. The theme API is very similar to the localization API, but of course these two concerns are orthogonal, and some applications support both localization and themes.

First, configure the set of supported themes:

<theme:theme-selector cookie-enabled="true">
    <theme:available-themes>
        <value>default</value>
        <value>accessible</value>
        <value>printable</value>
    </theme:available-themes>
</theme:theme-selector>

Note that the first theme listed is the default theme.

Themes are defined in a properties file with the same name as the theme. For example, the default theme is defined as a set of entries in default.properties. For example, default.properties might define:

css ../screen.css
template /template.xhtml

Usually the entries in a theme resource bundle will be paths to CSS styles or images and names of facelets templates (unlike localization resource bundles which are usually text).

Now we can use these entries in our JSP or facelets pages. For example, to theme the stylesheet in a facelets page:

<link href="#{theme.css}" rel="stylesheet" type="text/css" />

Or, when the page definition resides in a subdirectory:

<link href="#{facesContext.externalContext.requestContextPath}#{theme.css}" 
    rel="stylesheet" type="text/css" />

Most powerfully, facelets lets us theme the template used by a <ui:composition>:

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    template="#{theme.template}">

Just like the locale selector, there is a built-in theme selector to allow the user to freely switch themes:

<h:selectOneMenu value="#{themeSelector.theme}">
    <f:selectItems value="#{themeSelector.themes}"/>
</h:selectOneMenu>
<h:commandButton action="#{themeSelector.select}" value="Select Theme"/>

The locale selector, theme selector and timezone selector all support persistence of locale and theme preference to a cookie. Simply set the cookie-enabled property in components.xml:

<theme:theme-selector cookie-enabled="true">
    <theme:available-themes>
        <value>default</value>
        <value>accessible</value>
        <value>printable</value>
    </theme:available-themes>
</theme:theme-selector>

<international:locale-selector cookie-enabled="true"/>