Added translation support with react-imp. Added partial Polish translation.

src/index.tsx

@@ -1,21 +1,35 @@
+import * as locale_en from 'react-intl/locale-data/en';
+import * as locale_pl from 'react-intl/locale-data/pl';
+import * as messages_pl from './translations/pl.json';
 import * as React from 'react';
 import * as ReactDOM from 'react-dom';
+import {addLocaleData} from 'react-intl';
 import {ChartView} from './chart_view';
 import {HashRouter as Router, Route, Switch} from 'react-router-dom';
+import {IntlProvider} from 'react-intl';
 import {Intro} from './intro';
 import {TopBar} from './top_bar';
-import 'semantic-ui-css/semantic.min.css';
 import './index.css';
+import 'semantic-ui-css/semantic.min.css';
+
+addLocaleData([...locale_en, ...locale_pl]);
+
+const messages = {
+  pl: messages_pl,
+};
+const language = navigator.language && navigator.language.split(/[-_]/)[0];
 
 ReactDOM.render(
-  <Router>
-    <div className="root">
-      <Route component={TopBar} />
-      <Switch>
-        <Route exact path="/" component={Intro} />
-        <Route exact path="/view" component={ChartView} />
-      </Switch>
-    </div>
-  </Router>,
+  <IntlProvider locale={language} messages={messages[language]}>
+    <Router>
+      <div className="root">
+        <Route component={TopBar} />
+        <Switch>
+          <Route exact path="/" component={Intro} />
+          <Route exact path="/view" component={ChartView} />
+        </Switch>
+      </div>
+    </Router>
+  </IntlProvider>,
   document.querySelector('#root'),
 );