feat: add multilingual mode support (#241)

BREAKING CHANGE:  Layout file renamed ´layouts/partials/page-footer.html → layouts/partials/menu-nextprev.html`. If you use overrides, you might need to change the filenames as well.

layouts/partials/menu.html

@@ -3,7 +3,7 @@
 
 
   <section class="gdoc-nav--main">
-    <h2>Navigation</h2>
+    <h2>{{ i18n "nav_navigation" }}</h2>
     {{ if .Site.Params.GeekdocMenuBundle }}
       {{ partial "menu-bundle" (dict "current" . "source" .Site.Data.menu.main.main) }}
     {{ else }}
@@ -13,7 +13,7 @@
 
   {{ if and (in (slice "posts" "tags") .Section) (default false .Site.Params.GeekdocTagsToMenu) }}
     <section class="gdoc-nav--tags">
-      <h2>Tags</h2>
+      <h2>{{ i18n "nav_tags" }}</h2>
       <ul class="gdoc-nav__list">
         {{ $currentPage := .RelPermalink }}
         {{ range $name, $taxonomy := .Site.Taxonomies.tags }}
@@ -35,7 +35,7 @@
 
   <section class="gdoc-nav--more">
     {{ if .Site.Data.menu.more.more }}
-      <h2>More</h2>
+      <h2>{{ i18n "nav_more" }}</h2>
       {{ partial "menu-bundle" (dict "current" . "source" .Site.Data.menu.more.more) }}
     {{ end }}
   </section>