add chinese subtitles

ios/OralTrainer/Views/PlayerSectionView.swift

@@ -7,6 +7,8 @@ struct PlayerSectionView: View {
     @Binding var continuousPlayback: Bool
     var showsSubtitle: Binding<Bool>? = .constant(true)
     var showsLessonTitle: Bool = true
+    var showChineseSubtitles: Binding<Bool>? = nil
+    var chineseSubtitlePlaceholder: String = "正在翻译中文字幕…"
     var onFullscreen: () -> Void
 
     @State private var progressDragging = false
@@ -93,14 +95,34 @@ struct PlayerSectionView: View {
                 }
                 .padding(.vertical, 2)
             }
+            if let showChineseSubtitles = showChineseSubtitles {
+                HStack(spacing: 0) {
+                    Text("中文字幕")
+                        .font(.system(size: 13, weight: .bold))
+                        .foregroundColor(Theme.textSubtle)
+                    Spacer()
+                    Toggle("", isOn: showChineseSubtitles)
+                        .labelsHidden()
+                        .tint(Theme.accent)
+                }
+                .padding(.vertical, 2)
+            }
             Text(sentenceMetaText)
                 .font(.system(size: 13))
                 .foregroundColor(Theme.textSubtle)
             HStack(alignment: .center, spacing: 8) {
-                Text(sentenceTextText)
-                .font(.system(size: 15))
-                    .foregroundColor(.white)
-                    .lineLimit(4)
+                VStack(alignment: .leading, spacing: 4) {
+                    Text(sentenceTextText)
+                        .font(.system(size: 15))
+                        .foregroundColor(.white)
+                        .lineLimit(4)
+                    if let chineseSubtitleText = chineseSubtitleText {
+                        Text(chineseSubtitleText)
+                            .font(.system(size: 14))
+                            .foregroundColor(Theme.textMuted)
+                            .lineLimit(4)
+                    }
+                }
                 Spacer()
                 Button {
                     guard let sentence = controller.currentSentence, !(sentence.text ?? "").isEmpty else {
@@ -205,6 +227,20 @@ struct PlayerSectionView: View {
         }
     }
 
+    private var chineseSubtitleText: String? {
+        guard showChineseSubtitles?.wrappedValue == true else {
+            return nil
+        }
+        if let zh = controller.currentSentence?.zhText?.trimmingCharacters(in: .whitespacesAndNewlines),
+           !zh.isEmpty {
+            return zh
+        }
+        if (controller.currentSentence?.text ?? "").trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
+            return nil
+        }
+        return chineseSubtitlePlaceholder
+    }
+
     private var statusText: String {
         if let message = controller.cacheState.statusMessage {
             return message