Add remark on designer file namespace conflict (#34318)

Author: guardrex

aspnetcore/blazor/globalization-localization.md

@@ -1670,12 +1670,25 @@ To further understand how the Blazor framework processes localization, see the [
 
 To create localization shared resources, adopt the following approach.
 
+* Confirm that the [`Microsoft.Extensions.Localization`](https://www.nuget.org/packages/Microsoft.Extensions.Localization) package is referenced by the project.
+
+  [!INCLUDE[](~/includes/package-reference.md)]
+
+* Confirm that the <xref:Microsoft.Extensions.Localization?displayProperty=fullName> namespace is available to the project's Razor components via an entry in the project's `_Imports` file:
+
+  ```razor
+  @using Microsoft.Extensions.Localization
+  ```
+
 * Create a dummy class with an arbitrary class name. In the following example:
 
   * The app uses the `BlazorSample` namespace, and localization assets use the `BlazorSample.Localization` namespace.
   * The dummy class is named `SharedResource`.
   * The class file is placed in a `Localization` folder at the root of the app.
 
+  > [!NOTE]
+  > Don't use an autogenerated designer file (for example, `SharedResources.Designer.cs`). The dummy class is meant to act as the shared resource class. The presence of a designer file results in a namespace collision.
+
   `Localization/SharedResource.cs`:
 
   ```csharp