Added DeepL source culture

I18N Commander/UI WinForms/Components/Setting.cs

@@ -150,6 +150,59 @@ public sealed partial class Setting : UserControl
         return new Setting(settingData);
     }
 
+    internal readonly record struct ComboBoxItem(string DisplayText, int CultureIndex)
+    {
+        public override string ToString() => this.DisplayText;
+    }
+    
+    private static async Task<Setting> ShowDeepLSourceCultureSettingAsync()
+    {
+        var currentSourceCultureIndex = await AppSettings.GetDeepLSourceCultureIndex();
+        
+        // We load the corresponding culture for that index. As dropdown items, we show
+        // all other available cultures:
+        var allCultures = await AppSettings.GetCultureInfos();
+        var sourceCulture = allCultures.FirstOrDefault(n => n.Index == currentSourceCultureIndex);
+        
+        // Attention: We have to store the culture's index, because the index is not
+        // continuous and can change when the user adds or removes a culture!
+        var settingData = new SettingUIData(
+            Icon: Icons.icons8_chat_bubble_512,
+            SettingName: () => "DeepL Source Culture",
+            SettingExplanation: () => "The source culture is used to translate the missing translations.",
+            SetupDataControl: () =>
+            {
+                var dropdown = new ComboBox();
+                var currentCultureDropdownIndex = 0;
+                for (var n = 0; n < allCultures.Count; n++)
+                {
+                    var cultureInfo = allCultures[n];
+                    if(cultureInfo.Index == currentSourceCultureIndex)
+                        currentCultureDropdownIndex = n;
+
+                    dropdown.Items.Add(new ComboBoxItem($"{cultureInfo.Index}.: {cultureInfo.Code}", cultureInfo.Index));
+                }
+
+                dropdown.SelectedIndex = currentCultureDropdownIndex;
+                
+                // Setup the change event handler:
+                dropdown.SelectedValueChanged += async (sender, args) =>
+                {
+                    if(dropdown.SelectedItem is ComboBoxItem selectedItem)
+                        await AppSettings.SetDeepLSourceCultureIndex(selectedItem.CultureIndex);
+                };
+                
+                // Apply the desired layout:
+                dropdown.Dock = DockStyle.Fill;
+                dropdown.DropDownStyle = ComboBoxStyle.DropDownList;
+                
+                return dropdown;
+            }
+        );
+        
+        return new Setting(settingData);
+    }
+
     private static IEnumerable<Task<Setting>> ShowCultureSettingsAsync()
     {
         var isFirstCulture = true; // We need this flag to distinguish the first task from the others.
@@ -206,6 +259,7 @@ public sealed partial class Setting : UserControl
 
     public static IEnumerable<Task<Setting>> GetAllSettings()
     {
+        yield return ShowDeepLSourceCultureSettingAsync();
         foreach (var setting in ShowCultureSettingsAsync())
         {
             yield return setting;