add chinese subtitles

ios/OralTrainer/Views/FullscreenPlayerView.swift

@@ -4,6 +4,8 @@ import SwiftUI
 struct FullscreenPlayerView: View {
     @ObservedObject var controller: PlayerController
     var showsLessonTitle: Bool = true
+    var showChineseSubtitles: Bool = false
+    var chineseSubtitlePlaceholder: String = "正在翻译中文字幕…"
     let onExit: () -> Void
 
     @State private var subtitleVisible = true
@@ -66,10 +68,18 @@ struct FullscreenPlayerView: View {
                             .font(.system(size: 13))
                             .foregroundColor(Theme.textOverlay)
                         HStack(alignment: .center, spacing: 8) {
-                            Text(sentenceTextText)
-                            .font(.system(size: 15))
-                            .foregroundColor(.white)
-                            .lineLimit(2)
+                            VStack(alignment: .leading, spacing: 4) {
+                                Text(sentenceTextText)
+                                    .font(.system(size: 15))
+                                    .foregroundColor(.white)
+                                    .lineLimit(2)
+                                if let chineseSubtitleText = chineseSubtitleText {
+                                    Text(chineseSubtitleText)
+                                        .font(.system(size: 14))
+                                        .foregroundColor(Theme.textOverlay)
+                                        .lineLimit(2)
+                                }
+                            }
                             Spacer()
                             Button {
                                 guard let sentence = controller.currentSentence,
@@ -203,6 +213,20 @@ struct FullscreenPlayerView: View {
         }
     }
 
+    private var chineseSubtitleText: String? {
+        guard showChineseSubtitles 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