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Localization Basics

  • 6 minutes to read

The eXpressApp Framework allows you to localize your WinForms, ASP.NET Web Forms, and ASP.NET Core Blazor applications. All strings in the UI are read from the Application Model. Some properties in the Application Model are localizable, i.e., they can have different values depending on their language. For instance, generally the Caption property of any Application Model node is localizable. In this topic, you will learn how to use these properties to localize your applications. To see how a WinForms and ASP.NET Web Forms application can be localized, refer to the Localization section in the FeatureCenter demo, which is supplied with XAF. This demo is located in the %PUBLIC%\Documents\DevExpress Demos 23.1\Components\XAF\FeatureCenter.NETFramework.XPO folder by default.

UI Elements to be Localized

All UI elements related to data presentation and functionalities can be localized: View Item captions, List View column captions, business object captions, Action captions and Action item captions, and so on. For this purpose, the Application Model’s appropriate nodes have the localizable Caption property.

In addition, UI elements such as messages, exceptions, button captions, form captions, etc., can also be localized. For this purpose, the Application Model has the special Localization node. This node’s child nodes represent groups of the listed elements. Each group item has the Value property that can be localized.

If you extend the Application Model with new properties, you can specify which properties are to be localized. Refer to the Application Model Structure topic to learn how to do this. You can also localize custom string constants via the Localization node. Refer to the How to: Localize Custom String Constants topic to learn how.

General Information

To localize the user interface, use the Model Editor. There you will find the Language combo box on the Model Editor Toolbar.


By default, the drop-down list contains two options: (Default language) and Languages Manager…. The (Default language) option corresponds to the default language (English), but not to any country/region. To add more language options, select the Languages Manager…. In the invoked dialog, add the desired languages.



You can use a specific language (such as “fr-FR”), rather than a neutral language (such as “fr”). The specific language is recommended, because formatting options (e.g., currencies) can be different for cultures that speak the same language (e.g., for France, Belgium and Luxembourg). See the Culture-Specific Formatting topic for details.

Restart the Visual Studio and select the required language using the Language combo-box within the toolbar.


You can setup as many languages as you want. All the changes for a particular language are saved to the corresponding Model.DesignedDiffs.Localization.<language code>.xafml or Model<language code>.xafml_ file. These files resemble the Model.DesignedDiffs.xafml and Model.xafml files, which store the changes made in the Application Model in the default language (English). The changes stored in the Model.DesignedDiffs.Localization.<language code>.xafml and Model<language code>.xafml_ files are also superimposed on the previous model layer. To view these changes, right-click one of these files and choose View Code. For information about files with changes and layers of the Application Model, refer to the Application Model Basics topic.

Refer to the How to: Localize an XAF Application topics to learn more about the application localization process.

Ways to Specify an Application Language

In the Application Model

To specify the language in which your application will run, invoke the Model Editor, navigate to the Application node and set the required language for the IModelApplication.PreferredLanguage property. The following options are available.

  • (Default language)

    None of the generated Model.DesignedDiffs<language code>.xafml_ and Model<language code>.xafml_ files will be considered. All localizable elements will be set to the values specified in the Model.DesignedDiffs.xafml and Model.xafml files.

  • (User language)

    The values from the Model.DesignedDiffs<language code>.xafml_ and Model<language code>.xafml_ files will be superimposed on the values from the files with the default language (Model.DesignedDiffs.xafml and Model.xafml). In Windows Forms applications, the <language code> is taken from the operating system settings. In ASP.NET Web Forms applications, the <language code> is determined by browser preferences. If there are no appropriate Model.DesignedDiffs<language code>.xafml_ and Model<language code>.xafml_ files, only default values will be applied.

  • Certain Language

    The values from the Model.DesignedDiffs<language code>.xafml_ and Model<language code>.xafml_ files, which correspond to the specified language, will be superimposed.

In code

If you need to set the preferred language in dependence to a condition, handle the XafApplication.CustomizeLanguage event. Note that the language you set in this event handler cannot be changed via the Application Model at runtime.

Localization Rules

When building a UI, the system uses the appropriate language-specific xafml files. For instance, if German must be used in an application, the system uses the Model_de.xafml xafml file, where properties are set to German values. However, some values might not be found in language-specific xafml files. This may occur if you omitted a property when you were localizing your application to the required language. In this instance, there are two rules with which to get the value.

  • If the property, whose localized value is not found, is not calculated from another property, its value is taken from the xafml file in the default language.


  • If the property, whose localized value is not found, is calculated from another property, the localized value of the source property is taken. However, if the source property’s localized value is not found, the calculated property’s value is taken from the xafml file in the default language (dotted arrow in the image below).


The list of supported languages can be retrieved from these sources:

  1. The Languages key from the configuration file’s appSettings section:

        <!-- ... -->
        <add key="Languages" value="en;de;fr" />
        <!-- ... -->
      <!-- ... -->

    The value of this key consists of available language codes, separated by a semicolon.

  2. For ASP.NET Core Blazor UI applications. From appsettings.json. This languages list is used to:

    The first language in this list is used as a default language and is specified in the RequestLocalizationOptions.SupportedCultures.

        "DevExpress": { 
            "ExpressApp": { 
                "Languages": "en;de;fr" 
                 // ...
  3. From the current project/application differences file names.


When the Model Editor is invoked as the Visual Studio designer, only the last source is available. At runtime, these sources are joined. So, if there are no differences for a certain language, but this language is added in the configuration file, then this language can be specified as preferred, and the values stored in the corresponding satellite assembly will be used in the UI.


To load localized property values from satellite assemblies, the Visual Studio or running application must be restarted. When the language is added, but satellite assemblies are unavailable, you can get the System.IO.FileNotFoundException exceptions while debugging. These exceptions are properly handled internally, and do not cause the application crash at runtime. To skip these exceptions automatically, click the Debug | Exceptions… item in Visual Studio menu and uncheck Common Language Runtime Exceptions | System.IO.

See Also