fix issue with dropdowns key accessibility

src/app/navbar/expandable-navbar-section/expandable-navbar-section.component.html

@@ -1,4 +1,5 @@
 <li class="nav-item dropdown"
+    (keyup.enter)="activateSection($event)"
     (mouseenter)="activateSection($event)"
     (mouseleave)="deactivateSection($event)">
     <a href="#" class="nav-link dropdown-toggle" routerLinkActive="active"

src/app/shared/lang-switch/lang-switch.component.html

@@ -7,7 +7,7 @@
     <i class="fas fa-globe-asia fa-lg fa-fw"></i>
   </a>
   <ul ngbDropdownMenu class="dropdown-menu" [attr.aria-label]="'nav.language' |translate">
-    <li class="dropdown-item" #langSelect *ngFor="let lang of translate.getLangs()"
+    <li class="dropdown-item" tabindex="0" #langSelect *ngFor="let lang of translate.getLangs()"
             (click)="useLang(lang)"
             [class.active]="lang === translate.currentLang">
                 {{ langLabel(lang) }}