Swift 两个avspeech语句没有排队

当按下一个按钮时，我试图让两种语言的字符串（en和fr）在彼此之后读取。不幸的是，其中只有一个是发声的。我尝试了很多方法，但都没有成功（Xcode版本12.0、Mac OS 10.15.6、ios 14和13.1）。以下是我尝试的代码：

    func readTextNew(audioLanguage1: String, textToRead1: String, audioLanguage2: String, textToRead2: String) {
        //try? AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [])
        
        let synthesizer1 = AVSpeechSynthesizer()
        //synthesizer1.delegate = self
        let utterance1 = AVSpeechUtterance(string: textToRead1)
        utterance1.voice = AVSpeechSynthesisVoice(language: audioLanguage1)
        utterance1.volume = 1
        
        let utterance2 = AVSpeechUtterance(string: textToRead2)
        utterance2.voice = AVSpeechSynthesisVoice(language: audioLanguage2)
        utterance2.volume = 1

        synthesizer1.speak(utterance1)
        synthesizer1.speak(utterance2)
   
    }

如果有任何解决这个问题的建议，我将不胜感激