Menu.jsx

import React from 'react'
import { connect } from 'react-redux'

const Menu = ({ lang, changeLanguage }) =>
    <div>
        <p>Current Language: {lang}</p>
        <button onClick={() => changeLanguage('en')}>English</button>
        <button onClick={() => changeLanguage('fr')}>French</button>
    </div>
    
const mapStateToProps = state => ({
  lang: state.lang
})
const mapDispatchToProps = dispatch => ({
  changeLanguage: lang => dispatch({ type: 'CHANGE_LANGUAGE', payload: lang })
})
export default connect(
  mapStateToProps,
  mapDispatchToProps
)(Menu)