feat: Add internationalization (i18n) support (#182)

layouts/partials/toc.html

@@ -1,7 +1,7 @@
 {{ if (and $.Site.Data.config.enableToc (ne .Params.enableToc false) (gt .WordCount 250)) }}
 <aside class="mainTOC">
     <details {{ if $.Site.Data.config.openToc }}open {{ end }}>
-        <summary>Table of Contents</summary>
+        <summary>{{ i18n "toc" }}</summary>
         {{ .TableOfContents }}
     </details>
 </aside>