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For a multilingual application, it is common to display the content in the language that the end user prefers. Here we discuss the built-in support called internationalization labels.

However, if you prefer to use other approach, please refer to the Use Other Implementation section.

Internationalization Labels

The internationalization labels of an application are loaded from properties files based on the current locale[1]. A properties file is a simple text file encoded in UTF-8[2]. The file contains a list of key=value pairs, such as[3]

# This is the default file

By default the property file must be placed under the WEB-INF directory and named as[4], where lang is the language such as en and fr, and CNTY is the country, such as US and FR.

If you want to use one file to represent a language regardless the country, you could name it, such as Furthermore, is the default file if the user's preferred locale doesn't match any other file.

When an user accesses a page, ZK will load the properties files for the user's locale. For example, assume the locale is de_DE, then it will search the following files and load them if found:


By default, one properties file is used to contain all labels of a given locale. If you prefer to split it to multiple properties files (such as one file per module), please refer to the Loading Labels from Multiple Resources section.

Also notice that all files match the given locale will be loaded and merged, and the property specified in, say, will override what are defined in if replicated. It also means if a label is the same in both de_DE and de, then you need only to specify in (and then it will be inherited when de_DE is used). Of course, you could specify it in both files.

  1. It is the value returned by Locales.getCurrent(). For more information, please refer to the Locale section.
  2. If you prefer a different charset, please refer to the Encoding Character Set section.
  3. Please refer to here for more details about the format of a properties file, such as the use of multiple lines and EL expressions.
  4. Notice the directory and filename is configurable. For more information, please refer ZK Configuration Reference: org.zkoss.util.label.web.location

Access Internationalization Labels In ZUML

Use labels

Since 5.0.7 and later, an implicit object called labels was introduced, such that you could access the internationalization labels (so-called internationalization labels) directly. For example, assume you have a label called app.title, and then you could:

<window title="${}">

The labels object is a map (java.util.Map), so you could access the label directly by the use of labels.whatever in an EL expression. Moreover, as shown above, you could access the label even if a key is named as (a string containing dot), such as app.title in the above example.

If the key is not a legal name, you could use labels['key'] to access, such as labels['foo-yet'].

When an internationalization label is about to be retrieved, one of will be loaded. For example, if the Locale is de_DE, then WEB-INF/ will be loaded. If no such file, ZK will try to load WEB-INF/ and WEB-INF/ in turn.

Notice that ZK groups the segmented labels as map. For example, ${} was resolved as a map containing two entries (title and description).

app.description=A super application

If you have a key named as the prefix of the other keys, you have to use $ to access it. For example, if the labels consist of keys a, a.b, etc., ${labels.a.$} is required to resolve the label with key named a.

For example, in properties file:

app.description=A super application


<window title="${$}"><!-- shows "Application" -->
<window title="${}"><!-- WRONG! -->

Use c:l('key')

With 5.0.6 or prior, you could, to get an internationalization label, use ${c:l('key')} in EL expression. For example,

<?taglib uri="" prefix="c"?>

<window title="${c:l('app.title')}">

Notice that the l function belongs to the TLD file called, so we have to specify it with the taglib directive as shown above.

Use c:l2('key') to format the message

If you'd like to use the label as a pattern to generate concatenated message with additional arguments (like java.text.MessageFormat does), you could use the l2 function

For example, let us assume we want to generate a full name based on the current Locale, then we could use ${c:l2('key',args)} to generate concatenated messages as follows.

<?taglib uri="" prefix="c"?>
<label value="${c:l2('fullname.format', fullname)}">

where we assume fullname is a string array (such as new String[] {"Jimmy", "Shiau"}).

Labels.getLabel(String, Object[]) assumes the content is a valid pattern accepted by MessageFormat, such as "{1}, {0}".

Access Internationalization Labels In Java

To access labels in Java code (including zscript), you could use Labels.getLabel(String), Labels.getLabel(String, Object[]) and others.

String username = Labels.getLabel("username");

Here is a more complex example. Let us assume we want to generate a full name based on the Locale, then we could use Labels.getLabel(String, Object[]) to generate concatenated messages as follows.

public String getFullName(String firstName, String lastName) {
   return Labels.getLabel("fullname.format", new java.lang.Object[] {firstName, lastName});

Labels.getLabel(String, Object[]) assumes the content is a valid pattern accepted by MessageFormat, such as "{1}, {0}".

Encoding character set

By default, the encoding of properties files are assumed to be UTF-8. If you prefer another encoding, please specify it in a library property called org.zkoss.util.label.web.charset. It also means all properties files must be encoded in the same character set.

For more information, please refer to ZK Configuration Reference.

Loading Labels from Multiple Resources

It is typical to partition the properties file into several modules for easy maintenance. Since 5.0.7 and later, you could specify the location for each of these properties file with the label-location element. For example,


Notice that, once you specify label-location, the default loading of /WEB-INF/ won't take place. In other words, only the properties files specified in the label-location elements are loaded. Thus, if you'd like to load /WEB-INF/ too, you have to add it to label-location with others.

Also notice that you don't have to and shall not specify the language, such as de_DE, in the path. ZK will try to locate the most matched one as described in the previous section.

In addition to the servlet path, you could specify a file path by starting with file://[1]. For example, file:///foo/ If the target environment is Windows, you could specify the drive too, such as file:///C:/myapp/ The advantage is that additional properties files could be added after the project has been built into a WAR file.


Notice that the configuration with a path related to the file system is better not to be part of WEB-INF/zk.xml, since it is easy to cause errors when deploying the application. Rather, it is better to be specified in the additional configuration file. The additional configuration file is also specified at the run time and could be located in the file system (rather than the WAR file). It can be done by specifying the path of the configuration file in a library property called org.zkoss.zk.config.path.

For 5.0.6 and older, you could use the approach described in the following section to load multiple properties files.

  1. For more information about the URI of a file, please refer to File URI scheme.

Loading from Database or Other Resources

If you prefer to put the internationalization labels in, say, database, you could extend the label loader to load labels from other locations, say database. It can be done by registering a locator, which must implement either LabelLocator or LabelLocator2. Then, invoke Labels.register(LabelLocator) or Labels.register(LabelLocator2) to register it[1].

If you can represent your resource in URL, you could use LabelLocator (as show below). If you have to load it by yourself, you could use LabelLocator2 and return an input stream (

Alernative 1: load as an input stream:

public class FooDBLocator implements org.zkoss.util.resource.LabelLocator2 {
    private String _field;
    public FooDBLocator(String field) {
        _field = field;
    public InputStream locate(Locale locale) {
        InputStream is = ... //load the properties from, say, database
        return is;
    public String getCharset() {
        return "UTF-8"; //depending the encoding you use

Alernative 2: load as an URL:

public class FooServletLocator implements org.zkoss.util.resource.LabelLocator {
    private ServletContext _svlctx;
    private String _name;
    public FooServletLocator(ServletContext svlctx, String name) {
        _svlctx = svlctx;
        _name = name;
    public URL locate(Locale locale) {
        return _svlctx.getResource("/WEB-INF/labels/" + name + "_" + locale + ".properties");

Then, we could register label locators when the application starts by use of WebAppInit as follows.

public class MyAppInit implements org.zkoss.zk.ui.util.WebAppInit {
    public void init(WebApp wapp) throws Exception {
        Labels.register(new FooDBLocator(("moduleX");
        Labels.register(new FooDBLocator(("moduleY");
        Labels.register(new FooServletLocator((ServletContext)wapp.getNativeContext(), "module-1");
        Labels.register(new FooServletLocator((ServletContext)wapp.getNativeContext(), "module-2");

where we assume moduleX and moduleY is the database table to load the properties, and and are two modules of messages you provide. Then, you configure it in WEB-INF/zk.xml as described in ZK Configuration Reference.

  1. For 5.0.7 and later, you could use the label-location element if the properties file is located in the file system or in the Web application as described in the previous section.

Reload Labels Dynamically

The internationalization labels are loaded when a locale is used at the first time. It won't be reloaded automatically if the file is modified. However, it is easy to force ZK to reload by the use of Labels.reset().

For example, you could prepare a test paging for reloading as follows.

<button label="Reload Labels" onClick="org.zkoss.util.resource.Labels.reset();execution.sendRedirect(null);"/>
Test result: ${foo} ${another.whatever}

Use Other Implementation

If you prefer to use other implementation (such as property bundle), you could implement a static method and map it with xel-method. Then, you could reference it in EL expressions. For example,

<?xel-method prefix="c" name="label" class="foo.MyI18Ns" 
  signature="java.lang.String label(java.lang.String)"?>
<window title="${c:label('app.title')}">

Version History

Last Update : 2014/5/13

Version Date Content
5.0.5 October 2010 LabelLocator2 was introduced.
5.0.7 March 2011 The labels object was introduced.

Copyright © Potix Corporation. This article is licensed under GNU Free Documentation License.

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