Make Blazor WASM respect current UI culture (#62905)

Author: dariatiurina

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyCultureProvider.cs

@@ -3,6 +3,7 @@
 
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
+using System.Linq;
 using System.Runtime.InteropServices.JavaScript;
 
 namespace Microsoft.AspNetCore.Components.WebAssembly.Hosting;
@@ -62,7 +63,7 @@ public virtual async ValueTask LoadCurrentCultureResourcesAsync()
             throw new PlatformNotSupportedException("This method is only supported in the browser.");
         }
 
-        var culturesToLoad = GetCultures(CultureInfo.CurrentCulture);
+        var culturesToLoad = GetCultures(CultureInfo.CurrentCulture, CultureInfo.CurrentUICulture);
 
         if (culturesToLoad.Length == 0)
         {
@@ -72,30 +73,47 @@ public virtual async ValueTask LoadCurrentCultureResourcesAsync()
         await WebAssemblyCultureProviderInterop.LoadSatelliteAssemblies(culturesToLoad);
     }
 
-    internal static string[] GetCultures(CultureInfo cultureInfo)
+    internal static string[] GetCultures(CultureInfo cultureInfo, CultureInfo? uiCultureInfo = null)
     {
-        var culturesToLoad = new List<string>();
-
         // Once WASM is ready, we have to use .NET's assembly loading to load additional assemblies.
         // First calculate all possible cultures that the application might want to load. We do this by
         // starting from the current culture and walking up the graph of parents.
         // At the end of the the walk, we'll have a list of culture names that look like
         // [ "fr-FR", "fr" ]
-        while (cultureInfo != null && cultureInfo != CultureInfo.InvariantCulture)
-        {
-            culturesToLoad.Add(cultureInfo.Name);
 
-            if (cultureInfo.Parent == cultureInfo)
+        var culturesToLoad = GetCultureHierarchy(cultureInfo);
+        if (cultureInfo != uiCultureInfo)
+        {
+            foreach (var culture in GetCultureHierarchy(uiCultureInfo))
             {
-                break;
+                if (!culturesToLoad.Contains(culture))
+                {
+                    culturesToLoad = culturesToLoad.Append(culture);
+                }
+                // If the culture is in the list, we can break because we found the common parent.
+                else
+                {
+                    break;
+                }
             }
-
-            cultureInfo = cultureInfo.Parent;
         }
 
         return culturesToLoad.ToArray();
     }
 
+    private static IEnumerable<string> GetCultureHierarchy(CultureInfo? culture)
+    {
+        while (culture != CultureInfo.InvariantCulture && culture != null)
+        {
+            yield return culture.Name;
+            if (culture == culture.Parent)
+            {
+                break;
+            }
+            culture = culture.Parent;
+        }
+    }
+
     private partial class WebAssemblyCultureProviderInterop
     {
         [JSImport("INTERNAL.loadSatelliteAssemblies")]

src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyCultureProviderTest.cs

@@ -24,6 +24,21 @@ public void GetCultures_ReturnsCultureClosure(string cultureName, string[] expec
         Assert.Equal(expected, actual);
     }
 
+    [Theory]
+    [InlineData("fr-FR", "tzm-Latn-DZ", new[] { "fr-FR", "fr", "tzm-Latn-DZ", "tzm-Latn", "tzm" })]
+    [InlineData("en-US", "en-GB", new[] { "en-US", "en", "en-GB" })]
+    [InlineData("fr-FR", null, new[] { "fr-FR", "fr" })]
+    public void GetCultures_ReturnCultureClosureWithUICulture(string cultureName, string uiCultureName, string[] expected)
+    {
+        // Arrange
+        var culture = cultureName != null ? new CultureInfo(cultureName) : null;
+        var uiCulture = uiCultureName != null ? new CultureInfo(uiCultureName) : null;
+        // Act
+        var actual = WebAssemblyCultureProvider.GetCultures(culture, uiCulture);
+        // Assert
+        Assert.Equal(expected, actual);
+    }
+
     [Fact]
     public void ThrowIfCultureChangeIsUnsupported_ThrowsIfCulturesAreDifferentAndICUShardingIsUsed()
     {

src/Components/test/E2ETest/Tests/WebAssemblyLocalizationTest.cs

@@ -35,4 +35,23 @@ public void CanSetCultureAndReadLocalizedResources(string culture, string messag
         var messageDisplay = Browser.Exists(By.Id("message-display"));
         Assert.Equal(message, messageDisplay.Text);
     }
+
+    [Theory]
+    [InlineData("en-US", "fr-FR", "Bonjour!")]
+    [InlineData("fr-FR", "en-US", "Hello!")]
+    public void CanSetCultureAndDifferentiateBetweenCurrentAndUICulture(string culture, string cultureUI, string message)
+    {
+        Navigate($"{ServerPathBase}/?culture={culture}&cultureUI={cultureUI}");
+
+        Browser.MountTestComponent<LocalizedText>();
+
+        var cultureDisplay = Browser.Exists(By.Id("culture-name-display"));
+        Assert.Equal($"Culture is: {culture}", cultureDisplay.Text);
+
+        var cultureUIDisplay = Browser.Exists(By.Id("culture-ui-display"));
+        Assert.Equal($"CultureUI is: {cultureUI}", cultureUIDisplay.Text);
+
+        var messageDisplay = Browser.Exists(By.Id("message-display"));
+        Assert.Equal(message, messageDisplay.Text);
+    }
 }

src/Components/test/testassets/BasicTestApp/LocalizedText.razor

@@ -1,2 +1,3 @@
 <h3 id="culture-name-display">Culture is: @System.Globalization.CultureInfo.CurrentCulture.Name</h3>
+<h3 id="culture-ui-display">CultureUI is: @System.Globalization.CultureInfo.CurrentUICulture.Name</h3>
 <p id="message-display">@Resources.Message</p>

src/Components/test/testassets/BasicTestApp/Program.cs

@@ -63,6 +63,7 @@ private static void ConfigureCulture(WebAssemblyHost host)
     {
         // In the absence of a specified value, we want the culture to be en-US so that the tests for bind can work consistently.
         var culture = new CultureInfo("en-US");
+        var cultureUI = new CultureInfo("en-US");
 
         Uri uri = null;
         try
@@ -77,12 +78,18 @@ private static void ConfigureCulture(WebAssemblyHost host)
         if (uri != null && HttpUtility.ParseQueryString(uri.Query)["culture"] is string cultureName)
         {
             culture = new CultureInfo(cultureName);
+            cultureUI = culture; // Default to the same culture for UI if not specified
+        }
+
+        if (uri != null && HttpUtility.ParseQueryString(uri.Query)["cultureUI"] is string cultureUIName)
+        {
+            cultureUI = new CultureInfo(cultureUIName);
         }
 
         // CultureInfo.CurrentCulture is async-scoped and will not affect the culture in sibling scopes.
         // Use CultureInfo.DefaultThreadCurrentCulture instead to modify the application's default scope.
         CultureInfo.DefaultThreadCurrentCulture = culture;
-        CultureInfo.DefaultThreadCurrentUICulture = culture;
+        CultureInfo.DefaultThreadCurrentUICulture = cultureUI;
     }
 
     // Supports E2E tests in StartupErrorNotificationTest