dependencies:
  tts: ^1.0.2

执行命令，获取该库：

flutter packages get

请支持原文：http://tryenough.com/flutter-tts

使用时引入头文件：

import 'package:tts/tts.dart';

2.创建tts_helper类，作为使用tts的帮助类

import 'package:tts/tts.dart';

import 'dart:async';
import 'dart:io';

/// Singleton tool class for tts

/// Use TtsHelper step:
///
/// Method : #isLanguageAvailable judge language, here language is _languageMap's values like "en-US",instead of the type of 'en' etc..
///
/// Method : #getTtsLanguage  help you convert "en" to "en-US".
///
/// Method : #setLanguage help you set Language , but "en-US" is default value
///
/// use example:
/// TtsHelper.instance.speak("speech content");
/// or
/// TtsHelper.instance.setLanguageAndSpeak("speech content", "en-US");
/// ...
class TtsHelper {

  // Locale to tss language map
  static final Map<String, String> _languageMap = {
    'en': "en-US",
    'zh': "zh-CN",
    "ar": "ar-SA",
    "cs": "cs-CZ",
    "da": "da-DK",
    "de": "de-DE",
    "el": "el-GR",
    "es": "es-ES",
    "fi": "fi-FI",
    "fr": "fr-CA",
    "he": "he-IL",
    "hi": "hi-IN",
    "hu": "hu-HU",
    "id": "id-ID",
    "it": "it-IT",
    "ja": "ja-JP",
    "ko": "ko-KR",
    "nl": "nl-BE",
    "no": "no-NO",
    "pl": "pl-PL",
    "pt": "pt-BR",
    "ro": "ro-RO",
    "ru": "ru-RU",
    "sk": "sk-SK",
    "sv": "sv-SE",
    "th": "th-TH",
    "tr": "tr-TR",
    'en-US': "en-US",
    'zh-CN': "zh-CN",
    "ar-SA": "ar-SA",
    "cs-CZ": "cs-CZ",
    "da-DK": "da-DK",
    "de-DE": "de-DE",
    "el-GR": "el-GR",
    "es-ES": "es-ES",
    "fi-FI": "fi-FI",
    "fr-CA": "fr-CA",
    "he-IL": "he-IL",
    "hi-IN": "hi-IN",
    "hu-HU": "hu-HU",
    "id-ID": "id-ID",
    "it-IT": "it-IT",
    "ja-JP": "ja-JP",
    "ko-KR": "ko-KR",
    "nl-BE": "nl-BE",
    "no-NO": "no-NO",
    "pl-PL": "pl-PL",
    "pt-BR": "pt-BR",
    "ro-RO": "ro-RO",
    "ru-RU": "ru-RU",
    "sk-SK": "sk-SK",
    "sv-SE": "sv-SE",
    "th-TH": "th-TH",
    "tr-TR": "tr-TR",
  };

  static final String _defaultL = "en-US";
  List<String> _languages;
  static TtsHelper _instance;
  static TtsHelper get instance => _getInstance();

  factory TtsHelper() =>_getInstance();

  static TtsHelper _getInstance() {
    if (_instance == null) {
      _instance = new TtsHelper._internal();
    }
    return _instance;
  }

  TtsHelper._internal() {
    // Initialize
    _initPlatformState();
  }

  _initPlatformState() async {
    _languages = await Tts.getAvailableLanguages();

    // If getAvailableLanguages is null, add "en-US" to _languages.
    if (_languages == null) {
      _languages = [_defaultL];
    }
    // Default set en-US language
    _setLanguage(_defaultL);
  }

  String _getTtsLanguage(String localeStr) {
    if(localeStr == null || localeStr.isEmpty ||
        !_languageMap.containsKey(localeStr)) {
      return _defaultL;
    }
    return _languageMap[localeStr];
  }

  // Return whether the result if set language is successful
  Future<bool> _setLanguage (String lang) async {
    String language = _getTtsLanguage(lang);
    if (language == null || language.isEmpty) {
      language = _defaultL;
    }
    if(Platform.isIOS &amp;& !_languages.contains(language)) {
      return false;
    }
    final bool isSet = await Tts.setLanguage(language);
    return isSet;
  }

  // Returns whether the supported language is supported
  Future<bool> _isLanguageAvailable (String language) async {
    final bool isSupport = await Tts.isLanguageAvailable(language);
    return isSupport;
  }

  void speak (String text) async {
    if (text == null || text.isEmpty) { return;}
    Tts.speak(text);
  }

  void setLanguageAndSpeak(String text, String language) async {
    String ttsL = _getTtsLanguage(language);
    var setResult = await _setLanguage(ttsL);
    if(setResult != null) {
      var available = await _isLanguageAvailable(ttsL);
      if(available != null) {
        speak(text);
      }
    }
  }

}

请支持原文：http://tryenough.com/flutter-tts

3.添加测试页面

import 'package:flutter_tts/tts_helper.dart';

import 'package:flutter/MATErial.dart';

class VoiceSetPage extends StatefulWidget {
  VoiceSetPage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _VoiceSetPageState createState() => _VoiceSetPageState();
}

class _VoiceSetPageState extends State<VoiceSetPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(

        backgroundColor: Colors.blue,
        title: Text(widget.title),
        elevation: 5.0, // shadow the bottom of AppBar
      ),
      body: Center(
        child: ListView(
          children: <Widget>[
            ListTile(
              title: Text(
                'test vioce',
                style: TextStyle(fontWeight: FontWeight.w500, fontSize: 20.0),
              ),
              onTap: () {
                showAlertDialog(context);
                TtsHelper.instance.setLanguageAndSpeak("你好我是声音播放器", "zh");
              },
            ),
            Divider(
              height: 1,
            )
          ],
        ),
      ),
    );
  }
}

void showAlertDialog(BuildContext context) {
  NavigatorState navigator =
  context.rootAncestorStateOfType(const TypeMatcher<NavigatorState>());
  debugPrint("navigator is null?" + (navigator == null).toString());
  showDialog(
      context: context,
      builder: (_) => new AlertDialog(
          title: new Text("Dialog Title"),
          content: new Text("This is my content"),
          actions: <Widget>[
            new FlatButton(
              child: new Text("CANCEL"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
            new FlatButton(
              child: new Text("OK"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            )
          ]));
}

4.在main中添加测试入口

import 'package:flutter/material.dart';
import 'package:flutter_tts/voice_set_page.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  void _incrementCounter() {
    Navigator.push(context, MaterialPageRoute(builder: (context) => VoiceSetPage(title: "Setting")));
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              '点击浮动按钮跳转到语音测试页',
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: '跳转',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

测试可用，希望能帮助到你。

请支持原文：http://tryenough.com/flutter-tts

完成demo下载地址：
http://tryenough.com/flutter-tts