Use `null` as the default locale, which resolves to the current system default locale (#1185)

DiscordChatExporter.Cli/Commands/Base/ExportCommandBase.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
-using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -118,8 +117,12 @@ public abstract class ExportCommandBase : DiscordCommandBase
     )]
     public string DateFormat { get; init; } = "MM/dd/yyyy h:mm tt";
 
-    [CommandOption("locale", Description = "Locale to use when formatting dates and numbers.")]
-    public string Locale { get; init; } = CultureInfo.CurrentCulture.Name;
+    [CommandOption(
+        "locale",
+        Description = "Locale to use when formatting dates and numbers. "
+            + "If not specified, the default system locale will be used."
+    )]
+    public string? Locale { get; init; }
 
     [CommandOption("utc", Description = "Normalize all timestamps to UTC+0.")]
     public bool IsUtcNormalizationEnabled { get; init; } = false;

DiscordChatExporter.Core/Exporting/ExportRequest.cs

@@ -8,6 +8,7 @@ using DiscordChatExporter.Core.Discord.Data;
 using DiscordChatExporter.Core.Exporting.Filtering;
 using DiscordChatExporter.Core.Exporting.Partitioning;
 using DiscordChatExporter.Core.Utils;
+using DiscordChatExporter.Core.Utils.Extensions;
 
 namespace DiscordChatExporter.Core.Exporting;
 
@@ -39,9 +40,9 @@ public partial class ExportRequest
 
     public bool ShouldReuseAssets { get; }
 
-    public string Locale { get; }
+    public string? Locale { get; }
 
-    public CultureInfo CultureInfo { get; }
+    public CultureInfo? CultureInfo { get; }
 
     public bool IsUtcNormalizationEnabled { get; }
 
@@ -58,7 +59,7 @@ public partial class ExportRequest
         bool shouldFormatMarkdown,
         bool shouldDownloadAssets,
         bool shouldReuseAssets,
-        string locale,
+        string? locale,
         bool isUtcNormalizationEnabled
     )
     {
@@ -83,7 +84,7 @@ public partial class ExportRequest
             ? FormatPath(assetsDirPath, Guild, Channel, After, Before)
             : $"{OutputFilePath}_Files{Path.DirectorySeparatorChar}";
 
-        CultureInfo = CultureInfo.GetCultureInfo(Locale);
+        CultureInfo = Locale?.Pipe(CultureInfo.GetCultureInfo);
     }
 }
 

DiscordChatExporter.Gui/Converters/LocaleToDisplayNameConverter.cs

@@ -9,13 +9,15 @@ public class LocaleToDisplayNameConverter : IValueConverter
 {
     public static LocaleToDisplayNameConverter Instance { get; } = new();
 
-    public object? Convert(object value, Type targetType, object parameter, CultureInfo culture) =>
-        value is string locale ? CultureInfo.GetCultureInfo(locale).DisplayName : null;
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture) =>
+        value is string locale && !string.IsNullOrWhiteSpace(locale)
+            ? CultureInfo.GetCultureInfo(locale).DisplayName
+            : "System default";
 
     public object ConvertBack(
-        object value,
+        object? value,
         Type targetType,
-        object parameter,
+        object? parameter,
         CultureInfo culture
     ) => throw new NotSupportedException();
 }

DiscordChatExporter.Gui/Services/SettingsService.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Globalization;
 using System.IO;
 using Cogwheel;
 using DiscordChatExporter.Core.Exporting;
@@ -21,7 +20,7 @@ public partial class SettingsService()
 
     public ThreadInclusionMode ThreadInclusionMode { get; set; } = ThreadInclusionMode.None;
 
-    public string Locale { get; set; } = CultureInfo.CurrentCulture.Name;
+    public string? Locale { get; set; }
 
     public bool IsUtcNormalizationEnabled { get; set; }
 

DiscordChatExporter.Gui/ViewModels/Dialogs/SettingsViewModel.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Linq;
+using DiscordChatExporter.Core.Utils.Extensions;
 using DiscordChatExporter.Gui.Models;
 using DiscordChatExporter.Gui.Services;
 using DiscordChatExporter.Gui.ViewModels.Framework;
@@ -37,10 +37,11 @@ public class SettingsViewModel(SettingsService settingsService) : DialogScreen
         set => settingsService.ThreadInclusionMode = value;
     }
 
+    // These items have to be non-nullable because WPF ComboBox doesn't allow a null value to be selected
     public IReadOnlyList<string> AvailableLocales { get; } = new[]
         {
-            // Current locale
-            CultureInfo.CurrentCulture.Name,
+            // Current locale (maps to null downstream)
+            "",
             // Locales supported by the Discord app
             "da-DK",
             "de-DE",
@@ -73,10 +74,12 @@ public class SettingsViewModel(SettingsService settingsService) : DialogScreen
             "ko-KR"
         }.Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
 
+    // This has to be non-nullable because WPF ComboBox doesn't allow a null value to be selected
     public string Locale
     {
-        get => settingsService.Locale;
-        set => settingsService.Locale = value;
+        get => settingsService.Locale ?? "";
+        // Important to reduce empty strings to nulls, because empty strings don't correspond to valid cultures
+        set => settingsService.Locale = value.NullIfWhiteSpace();
     }
 
     public bool IsUtcNormalizationEnabled