npm install vue vue-i18n --save

import Vue from 'vue'
import App from './App'
import VueI18n from 'vue-i18n'

 
Vue.use(VueI18n) // 通过插件的形式挂载

const i18n = new VueI18n({
 locale: localStorage.getItem('locale') || 'zh-CN',
 //this.$i18n.locale // 通过切换locale的值来实现语言切换
 messages: {
  'zh-CN': require('./lang/zh'), // 中文语言包
  'en-US': require('./lang/en') // 英文语言包
 }
})

export const m = {
  welcome: '欢迎来到北京',
  today: '今天是',
  week: {
  sun: '星期日',
  mon: '星期一',
  tues: '星期二',
  wed: '星期三',
  thur: '星期四',
  fri: '星期五',
  sat: '星期六'
  }
}

export const m = { 
 welcome: 'Welcome to Beijing.',
 today: 'Today is ',
 week: {
 sun: 'Sunday',
 mon: 'Monday',
 tues: 'Tuesday',
 wed: 'Wednesday',
 thur: 'Thursday',
 fri: 'Friday',
 sat: 'Saturday'
 }
}

new Vue({
 el: '#app',
 i18n,
 components: { App },
 template: '<App/>'
})

<button @click="changeLang">切换语言</button>
 <h1>{{$t('m.welcome')}}</h1>
 <h3>{{$t('m.today')}}{{weekname}}</h3>

changeLang() {
  this.lang = localStorage.getItem('locale') || 'zh-CN';
  
  if ( this.lang === 'zh-CN' ) {
   this.lang = 'en-US';
   this.$i18n.locale = this.lang;
  } else {
   this.lang = 'zh-CN';
   this.$i18n.locale = this.lang;
  }
  localStorage.setItem('locale', this.lang);
  let week = this.getWeek();
  this.weekname = week;
 },

getWeek() {
  let week = new Date().getDay(); 
  let day = 'm.week.sun';
  switch (week) {
  case 0:
   day = 'm.week.sun';
   break;
  case 1:
   day = 'm.week.mon';
   break;
  case 2:
   day = 'm.week.tues';
   break;
  case 3:
   day = 'm.week.wed';
   break;
  case 4:
   day = 'm.week.thur';
   break;
  case 5:
   day = 'm.week.fri';
   break;
  case 6:
   day = 'm.week.sat';
   break;
  }
  return this.$i18n.t(day);
 }