title: react router 4 redirect to first route when basename changes
body: <p>i'm using <code>BrowserRouter</code> for routing in react for i18n i need to set basename to <code>/fa/</code> for persian and <code>/</code> for english so i change basename dynamicly the problem is when basename changes Router path change to first route i was entered. <br>
  for example:
  <br>
  i enter app with this url : <code>app.com/companies/</code> then go to <code>app.com/investors/</code> after that i change language and basename will change to <code>/fa/</code> then i will get back to <code>app.com/fa/companies/</code> instead of <code>app.com/fa/investors</code> <br>
  This is how i set basename: <br></p>
  
  <pre><code>import { BrowserRouter as Router, Route, RouteProps, Switch } from 'react-router-dom'
  &lt;Router basename={this.props.language.isEnglish ? '/' : '/fa/'}&gt;
   // Routes...
  &lt;Router /&gt;
  </code></pre>
  
  <p>so how can i prevent from redirecting to first route. ?
  <br> is this a problem at all or this is how it should be ? <br>
  is there better way for i18n in react router (we don't use react-intl) ?</p>