Technically we can add support for as many languages as we want with internationalization, but for demonstration purposes I am going to show you how to make our add products page with Dutch language support:

In step 1, we just created a property file called messages_nl.properties. This file acts as a Dutch-based message source for all our externalized label messages in the addProducts.jsp file. In order to display the externalized label messages, we used the <spring:message > tag in our addProducts.jsp file.

But by default, the <spring:message > tag will read messages from the messages.properties file only; we need to make a provision for our end user to switch to the Dutch locale when they view the webpage, so that the label messages can come from the messages_nl.properties file. We provided such a provision through a locale-choosing link in addProducts.jsp, as mentioned in step 2:

<a href="?language=en" >English</a>|<a href="?language=nl"       >Dutch</a> 

In step 2, we created two links, one each to choose English or Dutch as the preferred locale. When the user clicks on one of these links, it will add a request parameter called language to the URL with the corresponding locale value. For example, when we click on the English link on the add products page at runtime, it will change the request URL to http://localhost:8080/webstore/products/add?language=en ; similarly if you click on the Dutch link, it will change the request URL to http://localhost:8080/webstore/products/add?language=nl .

In step 3, we created a SessionLocaleResolver bean in our web application context as follows:

@Bean 
public LocaleResolver localeResolver(){ 
   SessionLocaleResolver resolver = new SessionLocaleResolver(); 
   resolver.setDefaultLocale(new Locale("en")); 
    
   return resolver; 
} 

SessionLocaleResolver is the one that sets the locale attribute in the user's session. One important property of SessionLocaleResolver is defaultLocale. We assigned en as the value for the default locale, which indicates that by default our page should use English as its default locale.

In step 4, we created a LocaleChangeInterceptor bean and configured it in the existing interceptor list:

@Override 
public void addInterceptors(InterceptorRegistry registry) { 
   registry.addInterceptor(new ProcessingTimeLogInterceptor()); 
    
   LocaleChangeInterceptor localeChangeInterceptor = new LocaleChangeInterceptor(); 
   localeChangeInterceptor.setParamName("language"); 
   registry.addInterceptor(localeChangeInterceptor); 
} 

We assigned the string language as the value for the paramName property in LocaleChangeInterceptor. There is a reason for this because, if you notice, in step 2 when we created the locale choosing link in add products page (addProduct.jsp), we used the same parameter name as the request parameter within the <a> tag:

<a href="?language=en" >English</a>|<a href="?language=nl" >Dutch</a> 

This way we can give a hint to LocaleChangeInterceptor to choose the correct user-preferred locale. So whatever parameter name you plan to use in your URL, use the same name as the value for the paramName property in LocaleChangeInterceptor. One more thing: whatever value you have given to the language request parameter in the link should match the translation message source file suffix. For example, in our case we have created a Dutch translation message source file, messages_nl.properties; here the suffix is nl and messages.properties without any suffix is considered the default for the en suffix. That's why in step 2 we have given nl and en as the values for the language parameters for Dutch and English, respectively:

<a href="?language=en" >English</a>|<a href="?language=nl" >Dutch</a> 

So finally, when we run our application and enter the http://localhost:8080/webstore/market/products/add URL, you will see our regular add products page with two extra links in the top-right corner to choose the language.

Clicking on Dutch changes the request URL to http://localhost:8080/webstore/market/products/add?language=nl, which brings up the LocaleChangeInterceptor and reads the Dutch-based label messages from messages_nl.properties.

Note that, if we do not give a language parameter in our URL, Spring will use the default message source file (messages.properties) for translation; if we give a language parameter, Spring will use that parameter value as the suffix to identify the correct language message source file (messages_nl.properties).

As I already mentioned just for demonstration purposes, I have internationalized a single web page (addProducts.jsp). I encourage you to internationalize the product detail web page (product.jsp) in our project. You can use the Google translate service (https://translate.google.com/) to find out the Dutch translation for labels. Along with this, try to add language support for one more language of your choice.