hugo-theme-terminal/layouts/partials/language-menu.html

{{ $currentpage := .Page }}
<ul class="menu menu--desktop menu--language-selector">
  <li class="menu__trigger">{{ .Language.LanguageName }}&nbsp;▾</li>
  <li>
    <ul class="menu__dropdown">
      {{ range $.Site.Home.AllTranslations }}
      {{ if ne .Lang $currentpage.Language.Lang }}
        {{ if eq .Lang $.Site.Params.DefaultContentLanguage }}
	<li><a href="{{ strings.Substr $currentpage.RelPermalink 3 }}">{{ .Language.LanguageName }}</a></li>
        {{ else }}
          {{ if eq $currentpage.Language.Lang $.Site.Params.DefaultContentLanguage }}
	  <li><a href="/{{ .Lang }}{{ $currentpage.RelPermalink }}">{{ .Language.LanguageName }}</a></li>
          {{ else }}
	  <li><a href="/{{ .Lang }}{{ substr $currentpage.RelPermalink 3 }}">{{ .Language.LanguageName }}</a></li>
          {{ end }}
        {{ end }}
      {{ end }}
      {{ end }}
    </ul>
  </li>
</ul>