Address accessibility issue:

"Links must have discernible text"
https://dequeuniversity.com/rules/axe/4.8/link-name?application=AxeChrome

which in this case is due to this:
- To ensure all link text is visible to screen readers,
  link text cannot be hidden (e.g. with display: none or aria-hidden="true").

templates/locales-banner.njk

@@ -16,7 +16,7 @@ It receives:
                {% for l in languages %}
                 <li class="govuk-language-select__list-item">
                     <a href="{{lang2url.addLangToUrl(currentUrl, l.IsoCode, true)}}" lang={{l.IsoCode}} rel="alternate" class="govuk-link" >
-                        <span aria-hidden="true">{{l.Name}}</span>
+                        <span>{{l.Name}}</span>
                     </a>
                 </li>
                {% endfor %}