If you create Web pages that will be read by speakers of different languages, you must provide a way for readers to view the page in their own language. One approach is to re-create the page in each language. However, that approach can be labor intensive, error prone, and difficult to maintain as you change the original page.

ASP.NET provides a way for you to create a page that can obtain content and other data based on the preferred language setting for the browser or the user's explicit choice of language. Content and other data is referred to as resources and such data can be stored in resource files or other sources

In the ASP.NET Web page, you configure controls to get their property values from resources. At run time, the resource expressions are replaced by resources from the appropriate resource file.

Resource Files

A resource file is an XML file that contains the strings that you want to translate into different languages or paths to images. The resource file contains key/value pairs. Each pair is an individual resource. Key names are not case sensitive. For example, a resource file might contain a resource with the Button1 key and the Submit value.

You create a separate resource file for each language (for example, English and French) or for a language and culture (for example English [U.K.], English [U.S.]). Each localized resource file has the same key/value pairs; the only difference is that a localized resource file can contain fewer resources than the default resource file. Language fallback then handles loading the neutral or default resource.

Resource files in ASP.NET have an .resx extension. At run time, the .resx file is compiled into an assembly, which is sometimes referred to as a satellite assembly. Because the .resx files are compiled dynamically, in the same manner as ASP.NET Web pages, you do not have to create the resource assemblies. The compilation condenses several similar-language resource files into the same assembly.

When you create resource files, start by creating a base .resx file. For each language that you want to support, create a new file that has the same basic file name, but with a language or language and culture (culture name) as part of it. For a list of culture names, see CultureInfo. For example, you might create the following files:

WebResources.resx

The base resource file. This is the default, or fallback, resource file.
WebResources.es.resx

A resource file for Spanish.
WebResources.es-mx.resx

A resource file for Spanish (Mexico), specifically.
WebResources.de.resxВ В В

A resource file for German.

At run time, ASP.NET uses the resource file that is the best match for the setting of the CurrentUICulture property. The UI culture for the thread is set according to the UI culture of the page. For example, if the current UI culture is Spanish, ASP.NET uses the compiled version of the WebResources.es.resx file. If there is no match for the current UI culture, ASP.NET uses resource fallback; starting with resources for a specific culture, then a neutral culture, and then the default resource file. In this example, the default resource file is WebResource.resx.

Creating Resource Files for ASP.NET Web Sites

In ASP.NET, you can create resource files that have different scope. You can create resource files that are global, which means that you can read the resource file from any page or code that is in the Web site. You can also create local resource files, which store resources for a single ASP.NET Web page (.aspx file).

Global Resource Files

You create a global resource file by putting it in the reserved folder App_GlobalResources at the root of the application. Any .resx file that is in the App_GlobalResources folder has global scope. Additionally, ASP.NET generates a strongly typed object, which gives developers a simple way to programmatically access global resources.

Local Resource Files

A local resources file is one that applies to only one ASP.NET page (an ASP.NET page with the extension of .aspx, .ascx, .master, and so on). You put local resource files in folders that have the reserved name App_LocalResources. App_LocalResources folders can exist in any folder in the application, unlike the root App_GlobalResources folder. You associate a set of resources files to a specific Web page using the name of the resource file.

For example, if you have a page named Default.aspx in the App_LocalResources folder, you might create the following files:

Default.aspx.resx

The default local resource file, which is the fallback resource file, if no language match is found.
Default.aspx.es.resx

The resource file for Spanish, without culture information.
Default.aspx.es-mx.resx

The resource file for Spanish (Mexico), specifically.
Default.aspx.de.resx

The resource file for French, without culture information.

The base name of the file matches the page file name, followed by a language and culture name, and ending with the extension .resx. For a list of culture names, see CultureInfo.

Choosing Between Global and Local Resource Files

You can use any combination of global and local resource files in the Web application. Generally, you add resources to a global resource file when you want to share the resources between pages. Resources in global resource files are also strongly typed for when you want to access the files programmatically.

However, global resource files can become large, if you store all localized resources in them. Global resource files can also be more difficult to manage, if more than one developer is working on different pages but in a single resource file.

Local resource files make it easier to manage resources for a single ASP.NET Web page. But you cannot share resources between pages. Additionally, you might create lots of local resource files, if you have many pages that must be localized into many languages. If sites are large with many folders and languages, using local resources can quickly expand the number of assemblies in the application domain.

When you make a change to a default resource file, either local or global, ASP.NET recompiles the resources and restarts the ASP.NET application, which can affect the overall performance of your site. Adding satellite resource files will not cause a recompilation of resources, but the ASP.NET application will restart.

Note
Linked resources are supported only in global resource files.

Working with Resources in Web Pages

After you create resource files, you can use them in ASP.NET Web pages. You typically use resources to fill the property values of controls on the page. For example, you might use resources to set the Text property of a Button control, instead of hard-coding the property to a specific string.

To use resources to set control property values, you can use implicit localization or explicit localization, as follows:

Implicit localization works with local resources and lets you automatically set control properties to matching resources.
Explicit localization lets you use a resource expression to set a control property to a specific resource in a local or global resource file.

Implicit Localization with Local Resources

If you have created local resource files for a specific page, you can use implicit localization to fill the property values for a control from the resource file. In implicit localization, ASP.NET reads a resource file and matches resources to property values.

To use implicit localization, you must use a naming convention for resources in the local resource file that uses the following pattern:

Key.Property

For example, if you are creating resources for a Button control named Button1, you might create the following key/value pairs in the local resource file:

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Button1.Text Button1.BackColor Label1.Text

You can use any name for Key, but Property must match a property of the control that you are localizing.

In the page, you use a special meta attribute in the markup for the control to specify implicit localization. You do not have to explicitly specify which properties are localized. A Button control that is configured for implicit localization might look similar to the following:

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<asp:Button ID="Button1" runat="server" Text="DefaultText" meta:resourcekey="Button1" />

The resourcekey value matches a key in the corresponding resource file. At run time, ASP.NET matches resources to control properties using the control label as the resourcekey. If a property value is defined in the resource file, ASP.NET substitutes the resource value for the property.

Explicit Localization

Alternatively, you can use explicit localization, where you use a resource expression. Unlike implicit localization, you must use a resource expression for each property that you want to set.

A Button control that is configured to set the Text property from a global resource file might look similar to the following:

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<asp:Button ID="Button1" runat="server" Text="<%$ Resources:WebResources, Button1Caption %>" />

The resource expression takes the following form, where Class is optional, unless the resource is a global one, and ResourceID is required:

<%$ Resources:Class, ResourceID %>

The Class value identifies the resource file to use when you use global resources. When .resx files are compiled, the base file name, without extensions, is used as the class name of the resulting assembly, explicitly. If you want to use resources from a local resource file (one that matches the current page name), you do not have to include a class name, because ASP.NET matches the page class to the resource class.

The ResourceID value is the identifier of the resource to read. In the preceding example, the Text property for the button is read from the global resource file WebResources.resx (or the appropriate localized version). In that file, ASP.NET uses the value for the resource with the identifier Button1Caption and for the page itself. To set page properties, you can use resource expressions in the @ Page directive.

Localizing Static Text

If your page includes static text, you can use ASP.NET localization by including it in a Localize control, and then using explicit localization to set the static text. The Localize control renders no markup; its only function is to act as a placeholder for localized text. The Localize control can be edited in design view, not only in the property grid. At run time, ASP.NET treats the Localize control as a Literal control. For example, your page might include the following code:

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<h1> <asp:Localize runat=server ID="WelcomeMessage" Text="Welcome!" meta:resourcekey="LiteralResource1" /> </h1> <br /> <br /> <asp:Localize runat="server" ID="NameCaption" Text="Name: " meta:resourcekey="LiteralResource2" /> <asp:TextBox runat="server" ID="TextBox1" meta:resourcekey="TextBox1Resource1" />

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<h1>
    <asp:Localize runat=server 
      ID="WelcomeMessage" 
      Text="Welcome!" meta:resourcekey="LiteralResource1" />
</h1>
<br />
<br />
<asp:Localize runat="server"
    ID="NameCaption"
    Text="Name: " meta:resourcekey="LiteralResource2" />
<asp:TextBox runat="server" ID="TextBox1" 
    meta:resourcekey="TextBox1Resource1" />

Selecting Resource Files for Different Languages

When a page is being run and ASP.NET is retrieving values from the resource manager, ASP.NET selects the version of the resource file that most closely matches the current UICulture setting for the page or uses resource fallback to obtain a resource. For example, if you are running the Default.aspx page and the current UICulture property is set to es (Spanish), ASP.NET uses the compiled version of the local resource file Default.aspx.es.resx.

ASP.NET can set the UICulture and Culture properties for the page to the language and culture values that are passed by the browser. Alternatively, you can set the UICulture and Culture properties explicitly, either declaratively or in code. You can also set the values declaratively in Web.config files. For detailed information, see How to: Set the Culture and UI Culture for ASP.NET Web Page Globalization.

Note
You should not rely exclusively on browser settings to set language and culture information, because users can be using a browser on a computer other than their own. Also, browsers frequently communicate only language, not a specific culture. In this case, the server has to deduce a specific culture for data formatting. A good strategy is to let users select a language explicitly.

Working with Resources Programmatically

Besides setting resource values in markup with resource expressions, you can retrieve resource values programmatically. You might do this, if the resource value is not known at design time or if you want to set the resource value based on a run-time condition. For detailed information, see How to: Retrieve Resource Values Programmatically.