Fix Custom Preset Label Handling On Language Change

UI/Window/RenderConfigWindow.cs

@@ -39,7 +39,7 @@ internal static class RenderConfigWindow
     /// </summary>
     private static RenderConfig? _uiConfig;
 
-    private static RenderConfig UiConfig => _uiConfig ??= new RenderConfig();
+    private static RenderConfig UIConfig => _uiConfig ??= new RenderConfig();
 
     // Controls cache for validation & sync
     private static O5Slider? _renderFpsSlider;
@@ -120,7 +120,7 @@ internal static class RenderConfigWindow
             ReloadPresetDropdown(GlobalSettings.Current.LastPresetName);
         }
         
-        var config = UiConfig;
+        var config = UIConfig;
         ApplyConfigToUI(config);
 
         SetWindowActive(true);
@@ -133,7 +133,7 @@ internal static class RenderConfigWindow
         var (_, scrollContent, _) =
             O5Factory.ScrollView(ctx, content, spacing: 10f, padding: 8f);
 
-        var config = UiConfig;
+        var config = UIConfig;
         EnsureDefaultConfig(config);
 
         double[] renderFpsSnap = { 23.976, 24, 29.97, 30, 59.94, 60, 144, 
@@ -843,7 +843,7 @@ internal static class RenderConfigWindow
 
     private static void TryGoRender()
     {
-        var config = UiConfig;
+        var config = UIConfig;
         SyncUItoConfig(config);
 
         // The encoders use 4:2:0 chroma subsampling, which needs an even width and height.
@@ -967,6 +967,13 @@ internal static class RenderConfigWindow
         }
     }
 
+    /// <summary>
+    /// Whether the text is the Custom label of any language. A preset with such a name could not be told apart
+    /// from the Custom entry of the dropdown after a language change.
+    /// </summary>
+    private static bool IsCustomPresetLabel(string text) =>
+        text == CustomPresetLabel || text == "(Modified)" || text == "(수정됨)";
+
     private static string CustomPresetLabel => LocalizationManager.Get("ui.render_config.preset_custom");
 
     private static void MarkConfigModified()
@@ -1018,7 +1025,7 @@ internal static class RenderConfigWindow
         SyncUItoConfig(config);
 
         var name = _presetNameInput?.Value.Trim();
-        if (string.IsNullOrWhiteSpace(name) || name == CustomPresetLabel)
+        if (string.IsNullOrWhiteSpace(name) || IsCustomPresetLabel(name))
         {
             CommonWarningDialogUI.ShowDialog(
                 LocalizationManager.Get("ui.render_config.validation_title"),
@@ -1200,13 +1207,10 @@ internal static class RenderConfigWindow
 
     private static void OnLanguageChanged(SystemLanguage language)
     {
-        if (_configWindow == null) return;
+        if (_configWindow == null || _presetDropdown == null) return;
 
-        if (_presetDropdown == null) return;
-
-        // The preset names are not localized, the Custom label is. The list is rebuilt from the preset names
-        // (which drops the Custom label of the previous language), then the label is decided from the values:
-        // the Custom label of the new language only when the values differ from the last loaded preset.
+        // The preset names are not localized, only the Custom label is. A dropdown value that is not a preset name
+        // is the Custom label (of the previous language), which is shown only while the values are modified.
         var names = PresetManager.GetPresets().Select(p => p.Name).ToList();
         if (names.Count == 0)
         {
@@ -1216,14 +1220,18 @@ internal static class RenderConfigWindow
             return;
         }
 
+        var current = _presetDropdown.Value;
+        var isModified = string.IsNullOrEmpty(current) || !names.Contains(current);
+
         _presetDropdown.SetValues(names);
-        var loadedName = _lastLoadedPresetName;
-        if (!string.IsNullOrEmpty(loadedName) && names.Contains(loadedName))
+        if (isModified)
         {
-            _presetDropdown.Set(loadedName, false);
+            MarkConfigModified();
+            return;
         }
 
-        UpdatePresetLabel(UiConfig);
+        _presetDropdown.Set(current, false);
+        UpdateDeleteButtonState();
     }
 
     private static string GetVersionText()