Workaround for that AVSpeechSynthesisVoice currentLanguageCode returns application language.

AVSpeechSynthesisVoice+iOS13Workaround.swift

extension AVSpeechSynthesisVoice {
    
    class func currentLanguageCodeWorkaround() -> String {
        if #available(iOS 13, *) {
            for preferredLanguage in Locale.preferredLanguages {
                let locale = Locale(identifier: preferredLanguage)
                
                if let languageCode = locale.languageCode {
                    var voiceLanguage = languageCode
                    if let regionCode = locale.regionCode {
                        voiceLanguage.append("-\(regionCode)")
                    }
                    if let avVoice = AVSpeechSynthesisVoice(language: voiceLanguage) {
                        return avVoice.language
                    }
                }
            }
            return "en-US"
        }
        else {
            return currentLanguageCode()
        }
    }
}