Messages may need to be formatted differently in different languages.

Use a MessageFormat object.

In English, for example, we say “file not found.” But in other languages the word order is different: the word for “not found” might need to precede the word for “file.” Java provides for this using the MessageFormat class. Suppose we want to format a message as follows:

$ java MessageFormatDemoIntl
At 3:33:02 PM on 01-Jul-00, myfile.txt could not be opened.
$ java -Duser.language=es MessageFormatDemoIntl
A 3:34:49 PM sobre 01-Jul-00, no se puede abrir la fila myfile.txt.
$

The MessageFormat in its simplest form takes a format string with a series of numeric indexes, and an array of objects to be formatted. The objects are inserted into the resulting string, where the given array index appears. Here is a simple example of a MessageFormat in action:

import java.text.*;

public class MessageFormatDemo {

    static Object[] data = {
            new java.util.Date(  ),
            "myfile.txt",
            "could not be opened"
    };

    public static void main(String[] args) {
        String result = MessageFormat.format(
            "At {0,time} on {0,date}, {1} {2}.", data);
        System.out.println(result);
    }
}

But we still need to internationalize this, so we’ll add some lines to our widget’s properties files. In the default (English) version:

# These are for MessageFormatDemo
#
filedialogs.cantopen.string=could not be opened
filedialogs.cantopen.format=At {0,time} on {0,date}, {1} {2}.

In the Spanish version, we’ll add these lines:

# These are for MessageFormatDemo
#
filedialogs.cantopen.string=no se puede abrir la fila
filedialogs.cantopen.format=A {0,time} sobre {0,date}, {2} {1}.

Then MessageFormatDemo needs to have a ResourceBundle, and get both the format string and the message from the bundle. Here is MessageFormatDemoIntl :

import java.text.*;
import java.util.*;

public class MessageFormatDemoIntl {

    static Object[] data = {
            new Date(  ),
            "myfile.txt",
            null
    };

    public static void main(String[] args) {
        ResourceBundle rb = ResourceBundle.getBundle("Widgets");
        data[2] = rb.getString("filedialogs.cantopen.string");
        String result = MessageFormat.format(
            rb.getString("filedialogs.cantopen.format"), data);
        System.out.println(result);
    }
}

There is more to the MessageFormat than this; see the Javadoc page for more details and examples.