- client: Make language tag in HTML same as setting language

Close #1797

Squashed commit of the following:

commit b822a83cb05cc5ba92000cdb7d1c12629471bc57
Merge: e2fa24fb 72ce5f57
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri Jul 3 11:02:56 2020 +0300

    Merge branch 'master' into fix/1797

commit e2fa24fb9fa0c15f8411e186e90e0ffb1c705fb2
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Thu Jul 2 18:21:30 2020 +0300

    Extract helper

commit ba8473e7b16ab8b1abbee4b42a4ef2b0de8c136b
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Thu Jul 2 15:31:42 2020 +0300

    - client: Make language tag in HTML same as setting language

client/src/components/App/index.js

@@ -36,6 +36,7 @@ import i18n from '../../i18n';
 import Loading from '../ui/Loading';
 import { FILTERS_URLS, MENU_URLS, SETTINGS_URLS } from '../../helpers/constants';
 import Services from '../Filters/Services';
+import { setHtmlLangAttr } from '../../helpers/helpers';
 
 class App extends Component {
     componentDidMount() {
@@ -62,6 +63,7 @@ class App extends Component {
         if (!processing) {
             if (language) {
                 i18n.changeLanguage(language);
+                setHtmlLangAttr(language);
             }
         }