AVFoundationフレームワークが必要
#import <AVFoundation/AVFoundation.h>
AVSpeechUtterance *utterance = [AVSpeechUtterance
speechUtteranceWithString:@"The quick brown fox"];
// 言語、省略時はiOS設定に従う
utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:@"en-US"];
utterance.rate = 0.2;
utterance.volume = 0.8;
AVSpeechSynthesizer *synth = [[AVSpeechSynthesizer alloc] init];
[synth speakUtterance:utterance];