Table of Contents
I'd like to thank Jean-Claude Manoli for developing his C# Code format, which Ii used in writing this tutorial.
Introduction
Developing websites to support multiple languages can be a challenging and time-consuming process. With standard HTML pages, this involves creating and maintaining duplicate versions of each page for each supported language as well as having the language content embedded into the HTML, where content can’t easily be edited. While the process improved slightly with the introduction of scripting technologies such as ASP and PHP, no significant development or maintenance time was saved. For those of you who have to develop multi-lingual interfaces and applications, you’ll be glad to know that ASP.NET makes things considerably easier.
ASP.NET and the .NET Framework ship with support for multilingual applications, namely in the form of Resource files, the CultureInfo class, and the System.Globalization and System.Resources.ResourceManager namespaces. Unfortunately, in its present state, localizing content in ASP.NET applications is still a tedious process. Like everything else in .NET though, the object model and sheer power available makes extending what's already available and developing new functionality to support better localization easy as 1 - 2 - 3.
In this first part, we'll develop a custom resource manager which avoids the limitation of .NET Assembly Resource Files as well as extend a number of classes to easily support localization. In the second part, we’ll spend more time talking about creating multilingual applications, specifically looking at database implementations and techniques.
By the end of this tutorial, you should be able to create multilingual applications with a minimum of work and maintenance, and be able to easily add new languages to it later on.
Before We Get Started
If you aren't familiar with localization in .NET, don't worry. This tutorial mostly skips what's available in .NET and talks about alternatives to make the job easier. There are a couple of core principals you should know though. (Even if you don't know the basics, you can skip this section and download the simple application I've created to showcase the core functionality, playing with it will probably be the best way to understand).
Basics
The way localization works in .NET is fairly straightforward. Content is stored in pretty simple XML files called Resource Files. You create a Resource File for each supported language (more can be added later on). When the application is compiled, the resource files are embedded into assemblies - the default resource file is embedded in the main assembly (.dll file); language-specific resource files are embedded into their own assemblies called satellite assemblies. Resource files are pretty simple and look a lot like a hashtable, they have a name and a value - the name is the same for all resource files, and the value is a language specific translation of some content. In essence, this allows you to use the System.Resources.ResourceManager class to do things like:
1: UserNameLabel.Text = myResourceManager.GetString("Username");
2: UserNameValidator.ErrorMessage =
myResourceManager.GetString("RequiredUsername");
The resource manager will automatically load the right resource file based on the current thread's CurrentCulture value - more on this in the next section. Hopefully, you are already seeing a lot of potential. Some of the key highlights are:
- Content is separated into simple XML files.
- There's a separate XML file for each supported language.
- The code to load values is relatively simple and short.
- The
ResourceManager class automatically retrieves the content from the right XML file based on the thread's CurrentCulture value. - You can easily have 1 actual page, for N supported languages.
Cultures
It's important to have a good understanding of Cultures since our new code will make use of them - specifically the System.Globalization.CultureInfo class, and the culture name value which follows the RFC 1766 naming standard. Basically, you create a new CultureInfo instance by specifying the culture name in the constructor:
1: CultureInfo c = new CultureInfo("en-US");
2: CultureInfo c = new CultureInfo("en-AU");
3: Cultureinfo c = new CultureInfo("he-IL");
Once you have a CultureInfo instance, you can set the current thread's UIculture to it, which will make your ResourceManager in the above code automatically fetch the content from the right XML resource file.
1: CultureInfo c = new CultureInfo("en-US");
2: System.Threading.Thread.CurrentThread.CurrentCulture = c;
3: System.Threading.Thread.CurrentThread.CurrentUICulture = c;
In part 2, we'll discuss ways to figure out which culture to load, but for now, it can be as simple as passing a code in the QueryString. For example, when lang=f is present, the French Canadian culture should be used. The other key factor is where to do all of this. The simplest and most logical place is in the Global.Asax's Begin_Request.
Download Dummy Application
The best way to understand the basics is to play with some code. I've created an extremely basic VB.NET web application to demonstrate the basic principles. Download it and play with it. Look at the structure of the 3 resource files, the codebehind for index.aspx, and the code in global.asax.
Why Not Use What's Available As-Is?
While it's certainly possible to develop a multilingual application with the tools provided with ASP.NET, there are a number of limitations which make the task less than streamlined. Some of the key problems are:
- Resource files are embedded into [satellite] assemblies
- Resource files can't return strongly-typed objects
- Web controls aren't easily hooked with resource files
While the list might seem small, the above three issues can be quite serious - with the first being the worst. For example, since resource files are embedded into assemblies, it's very difficult to ship a product which provides the client with the flexibility to change the content - a feature offered by many products. At my previous job, every time the translation department wanted to change some text, we'd need to recompile the entire application, stop 20 web servers, and copy the .dll into the bin folder - a frustrating process.
Building a Better Resource Manager
Our first task is to build a better Resource Manager which won't cause our Resource Files to be embedded into assemblies. This will allow Resource Files to be easily edited in a production or client environment. Our core functionality will be located in three functions:
- The
public method GetString which is used throughout the application to access the required resource. - The
private method GetResource which gets a HashTable either from the cache or by calling LoadResource. - The
private method LoadResource which parses the XML file and stores it into the cache.
GetString()
1: public static string GetString( string key) {
2: Hashtable messages = GetResource();
3: if (messages[key] == null){
4: messages[key] = string.Empty;
5: #if DEBUG
6: throw new ApplicationException("Resource" +
" value not found for key: " + key);
7: #endif
8: }
9: return (string)messages[key];
10: }
The method accepts a single argument, the key of the resource we want to get. It then retrieves a HashTable of content using GetResource, which is culture-aware and returns us the correct HashTable. If the requested key doesn’t exist, we’ll throw an exception if the application is in DEBUG mode, else we’ll simply return an empty string.
GetResource()
1: private static Hashtable GetResource() {
2: string currentCulture = CurrentCultureName;
3: string defaultCulture =
LocalizationConfiguration.GetConfig().DefaultCultureName;
4: string cacheKey = "Localization:" +
defaultCulture + ':' + currentCulture;
5: if (HttpRuntime.Cache[cacheKey] == null){
6: Hashtable resource = new Hashtable();
7:
8: LoadResource(resource, defaultCulture, cacheKey);
9: if (defaultCulture != currentCulture){
10: try{
11: LoadResource(resource, currentCulture, cacheKey);
12: }catch (FileNotFoundException){}
13: }
14: }
15: return (Hashtable)HttpRuntime.Cache[cacheKey];
16: }
The GetResource() method is slightly more complicated. Its goal is to retrieve a HashTable which can be looked up by a key to retrieve a value. The method will first look to see if the HashTable has already been loaded and cached [line: 5]. If so, it simply returns the value from the cache. Otherwise, it will use LoadResource() to parse the appropriate XML file [lines: 6-13]. Something worthy of noting is that the "appropriate XML file" is actually a mix of the XML file for the current culture as well as the one for the default culture. The default culture is specified in the configuration file [line: 3], and the current culture is retrieved from the current thread's current culture [line: 2].
First, the default culture is loaded [line: 8], and then the current culture is loaded [line: 11]. This means if a key is defined in both XML files (which most should be), the default value will be overridden by the culture-specific value. But if it doesn’t exist in the culture-specific value, the default value will be used.
LoadResource()
1: private static void LoadResource(Hashtable resource,
string culture, string cacheKey) {
2: string file =
LocalizationConfiguration.GetConfig().LanguageFilePath +
'\\' + culture + "\\Resource.xml";
3: XmlDocument xml = new XmlDocument();
4: xml.Load(file);
5: foreach (XmlNode n in xml.SelectSingleNode("Resource")) {
6: if (n.NodeType != XmlNodeType.Comment){
7: resource[n.Attributes["name"].Value] = n.InnerText;
8: }
9: }
10: HttpRuntime.Cache.Insert(cacheKey, resource,
new CacheDependency(file), DateTime.MaxValue, TimeSpan.Zero);
11: }
LoadResource loads the XML file [line: 4] (it gets the root path from our configuration file [line: 2]) and simply parses it while loading the values into our HashTable [line: 5 - 9]. Finally, the HashTable is stored in the Cache [line: 10].
Other Enhancements
Wrappers
There are a number of minor enhancements which can be done to our Resource Manager class. For example, I build bilingual webpages in English and French. Annoyingly, in English, a colon is always glued to the word it follows, but in French there has to be a space. For example:
Username:
Nom d'utilisateur : //French
This means, the colon needs to be localized. Instead of using the GetString() method, we can simply build a wrapper:
1: public static string Colon {
2: get { return GetString("colon"); }
3: }
In our English resource file, the colon would simply be ':', while in the French one, it would have a space ' :'.
Strongly-Typed Resources
The reason we use HashTable instead of a NameValueCollection is because the Resource Manager class can be expanded to return strongly-typed objects. For example, you might have localized help content which is more than just a single value. It might have a title, an example, and the help text. While exploring this is beyond the scope of this article (perhaps a part 3??), the capability exists.
Localized Controls
Our next goal is to make our life easier when developing a website by expanding existing server controls (literals, labels, buttons) to be localization-aware. We begin by creating a very simple interface our new controls will implement.
ILocalized
1: public interface ILocalized{
2: string Key {get; set; }
3: bool Colon {get; set; }
4: }
ILocalized defines a Key property which will be passed to our ResourceManager's GetString() method. In order to show how you can expand these classes to fit your own needs, I've also included a Colon property as a boolean, which will tell our controls if they should append a colon at the end of their value.
LocalizedLiteral
1: public class LocalizedLiteral : Literal, ILocalized {
2: #region fields and properties
3: private string key;
4: private bool colon = false;
5:
6: public bool Colon {
7: get { return colon; }
8: set { colon = value; }
9: }
10:
11: public string Key {
12: get { return key; }
13: set { key = value; }
14: }
15: #endregion
16:
17:
18: protected override void Render(HtmlTextWriter writer) {
19: base.Text = ResourceManager.GetString(key);
20: if (colon){
21: base.Text += ResourceManager.Colon;
22: }
23: base.Render(writer);
24: }
25: }
The first web control that we'll look at making localization-aware is the oft-used System.Web.UI.WebControls.Literal. First, we make our class inherit from the Literal control and inherit our ILocalized interface [line: 1]. Next, we implement the Key and Colon properties as defined in the ILocalized interface [line: 3 - 14]. Finally, we override the Render method of our base Literal class and use the ResourceManager's GetString() method and Colon property to fully localize our control [line: 19 - 22]. Don't forget to call the base class' Render() method afterwards to let it work its magic [line: 23].
Rinse, Wash and Repeater
You can copy and paste the same code over and over again and simply change the name of the class and what it inherits from; for example, let's do a localized button:
1: public class LocalizedButton : Button, ILocalized {
2:
3: #region Fields and Properties
4: private string key;
5: private bool colon = false;
6:
7: public string Key {
8: get { return key; }
9: set { key = value; }
10: }
11:
12: public bool Colon {
13: get { return colon; }
14: set { colon = value; }
15: }
16:
17: #endregion
18:
19: protected override void Render(HtmlTextWriter writer) {
20: base.Text = ResourceManager.GetString(key);
21: if (colon){
22: base.Text += ResourceManager.Colon;
23: }
24: base.Render(writer);
25: }
26: }
Notice that only the two bolded words have changed.
When desired, you can expand the functionality. For example, it isn't uncommon to have a LinkButton which pops up a JavaScript confirmation box when deleting something. We can easily achieve this by creating a 2nd key property:
1: using System.Web.UI;
2: using System.Web.UI.WebControls;
3:
4: namespace Localization {
5: public class LocalizedLinkButton : LinkButton, ILocalized {
6: #region Fields and Properties
7: private string key;
8: private bool colon;
9: private string confirmKey;
10:
11: public string ConfirmKey {
12: get { return confirmKey; }
13: set { confirmKey = value; }
14: }
15: public string Key {
16: get { return key; }
17: set { key = value; }
18: }
19: public bool Colon {
20: get { return colon; }
21: set { colon = value; }
22: }
23: #endregion
24:
25: protected override void Render(HtmlTextWriter writer) {
26: if(key != null){
27: Text = ResourceManager.GetString(key);
28: if (colon) {
29: Text += ResourceManager.Colon;
30: }
31: }
32: if (confirmKey != null) {
33: Attributes.Add("onClick", "return confirm('" +
ResourceManager.GetString(confirmKey).Replace("'",
"\'") + "');");
34: }
35:
36: base.Render(writer);
37: }
38:
39: }
40: }
Using Localized Controls
You use the localized controls like any other server control. First, register the control on the page:
1: <%@ Register TagPrefix="Localized"
Namespace="Localization" Assembly="Localization" %>
Then, without having to write any code, you can simply add the control either by drag and dropping it in the designer, or in the HTML mode by typing:
1: <Localized:LocalizedLiteral id="passwordLabel"
runat="server" Key="password" Colon="True" />
2: <Localized:LocalizedButton id="login"
runat="server" colon="false" Key="login" />
Download
The best thing to do now is to play a bit with some code. I've again created a sample site (similar to the previous one), but this time using our new Resource Manager class and Localized controls. You might need to change the web.config's languageFilePath property to point to the right folder.
History
- 8/14/2004: Initial version
License
This article has no explicit license attached to it, but may contain usage terms in the article text or the download files themselves. If in doubt, please contact the author via the discussion board below. A list of licenses authors might use can be found here.
